Memory device and a semiconductor device

ABSTRACT

The present invention provides a memory device and a semiconductor device which have high reliability for writing at low cost. Furthermore, the present invention provides a memory device and a semiconductor device having a non-volatile memory element in which data can be additionally written and which can prevent forgery due to rewriting and the like. The memory element includes a first conductive layer, a second conductive layer, and an organic compound layer, which is formed between the first conductive layer and the second conductive layer, and which has a photosensitized oxidation reduction agent which can be an excited state by recombination energy of electrons and holes and a substance which can react with the photosensitized oxidation reduction agent.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a memory device and a semiconductordevice equipped with a memory element formed by using an organiccompound.

2. Description of the Related Art

In recent years, a semiconductor device is required to be manufacturedat low cost. Therefore, an electronic device using an organic compoundin a control circuit, a memory circuit, or the like has been widelydeveloped. Furthermore, an organic EL (Electro-Luminescence), an organicTFT (thin film transistor), an organic semiconductor laser, and the likehave developed.

Moreover, a memory device having a memory element using an organiccompound has been developed, and a technique of writing data bygenerating interaction with an organic compound of the memory elementdue to the generation of internal light of the memory element so as tocause chemical change and changing conductivity in the memory element isproposed. To be concrete, an example of writing data by separatingchains of a conjugate molecule by an effect of internal light,heightening chemical reactivity of chemical species added by the effectof light, attacking a conductive material in a cell, and reducingconductivity of bulk is illustrated. (For example, reference 1: JP-T2001-503183 (page 10, FIG. 6)).

SUMMARY OF THE INVENTION

However, in the memory device shown in the reference 1, when aconjugated molecule is chain-separated by generation of internal lightso as to write data, a plurality of reaction products are formed sinceit is difficult to control a product generated due to chain separation.Moreover, when data is written by a technique of attacking a conductivematerial in a cell with chemical species in which chemical reactivity isheightened by the generation of the internal light and reducingconductivity of bulk, radical is generated and reaction is advanced.Thus, the stopping of the reaction is difficult to control; as a result,it is difficult to form an arbitrary product. Therefore, there areproblems that conductivity of a memory element after writing in can notbe controlled, variation in a written result is generated, and writingsuccess is reduced.

As a memory circuit, a DRAM (Dynamic Random Access Memory), a SRAM(Static Random Access Memory), an FeRAM (Ferroelectric Random AccessMemory), a mask ROM (Read Only Memory), an EPROM (ElectricallyProgrammable Read Only Memory), an EEPROM (Electrically Erasable andProgrammable Read Only Memory), a flash memory, and the like can begiven. Among them, in the case of a DRAM and an SRAM which are volatilememory devices, data is erased when the power is turned off so that datais required to be written every time the power is turned on. An FeRAM isa nonvolatile memory circuit which uses a capacitor element including aferroelectric layer and requires a large number of manufacturing steps.A mask ROM has a simple structure, however, data is required to bewritten during the manufacturing steps, and thus data cannot beadditionally written. An EPROM, an EEPROM, and a flash memory arenon-volatile memory devices using an element having two gate electrodes,so that the manufacturing steps are increased.

In view of the above problems, the present invention provides asemiconductor device with high reliability for writing at low cost.Furthermore, the present invention provides a semiconductor devicehaving a non-volatile memory element in which data can be additionallywritten and which can prevent forgery due to rewriting and the like.

The memory element included in the memory device of the presentinvention has a first conductive layer, a second conductive layer, andan organic compound layer, which is formed between the first conductivelayer and the second conductive layer and which has a photosensitizedoxidation reduction agent may come to an excited state by recombinationenergy of holes and electron and a substance which reacts with thephotosensitized oxidation reduction agent.

Note that a light emitting material may be included in the organiccompound layer.

In the memory element included in the memory device according to thepresent invention, data is written by applying voltage to the firstconductive layer and the second conductive layer, utilizingrecombination energy or emission energy caused by recombining holes andelectrons so that the photosensitized oxidation reduction agent is in anexcited state, using the excited state photosensitized oxidationreduction agent to have at least one part of the photosensitizedoxidation reduction reaction, and generating a reaction product which isdifferent in conductivity from a substance.

In the electrons and holes generated by applying voltage to the firstconductive layer and the second conductive layer in the memory element,recombination is performed in at least one selected from aphotosensitized oxidation reduction agent, a substance, or a lightemitting material, so that the photosensitized oxidation reduction agentcomes to an excited state by the recombination energy or light emissionenergy caused by the recombination, and at least one part of thesubstance has a photosensitized oxidation reduction reaction by thephotosensitized oxidation reduction agent in the excited state, therebya product is formed.

Note that the organic compound layer may be formed by laminating a layerformed of a light emitting material and a layer formed of aphotosensitized oxidation reduction agent and a substance.

Furthermore, either electrode of a light emitting element and eitherelectrode of a memory element are to be a common electrode, and thecommon electrode is formed of the material having a light-transmittingproperty, and therefore, a photosensitized oxidation reduction agent ofthe memory element can be irradiated with light emitted from the lightemitting element and the photosensitized oxidation reduction agent canbe in an excited state.

At least one of a charge injection layer and a charge transport layermay be provided between the first conductive layer and the organiccompound layer. Similarly, at least one of a charge injection layer anda charge transport layer may be provided between the second conductivelayer and the organic compound layer. When the first conductive layerfunctions as an anode, at least one of the hole injection layer and thehole transport layer may be provided between the first conductive layerand the organic compound layer. When the second conductive layerfunctions as a cathode, at least one of the electron injection layer andthe electron transport layer may be provided between the secondconductive layer and the organic compound layer.

A semiconductor device having the memory device may include a conductivelayer serving as an antenna and a transistor electrically connected tothe conductive layer. Furthermore, the semiconductor device having thememory device may include a diode connected to the first conductivelayer or the second conductive layer.

In the semiconductor device, a memory cell array and a write circuit areprovided over a glass substrate or a flexible substrate, and the writecircuit may be formed of a thin film transistor.

In the semiconductor device, the memory cell array and the write circuitare provided over a single crystal semiconductor substrate, and thewrite circuit may be formed of a field effect transistor.

Furthermore, in the semiconductor device, any one or more of a readoutcircuit, a power source circuit, a clock generation circuit, a datamodulation/demodulation circuit, a control circuit, and interfacecircuit may be included in addition to the write circuit.

As a typical example of a semiconductor device according to the presentinvention, a wireless chip typified by an ID chip, a wireless tag, anRFID (Radio frequency identification) tag, an IC tag, or the like can begiven.

In the memory element of the present invention, data is written byexciting a photosensitized oxidation reduction agent by recombinationenergy of holes and electrons, performing a photosensitized oxidationreduction reaction of a substance by the excited energy, and changingelectrical resistance of the memory element by generating a reactionproduct. Because of this, writing can be controlled; as a result,variation in writing can be reduced. Moreover, the writing success canbe increased.

Even if a light irradiation device for writing is not provided outside,a memory element emits light itself and data can be written in by usingthe light, and therefore, downsizing of a memory device and asemiconductor device is possible, and high integration is possible.Besides, since a photosensitized oxidation reduction agent can beexcited without loss of energy emitted from a light emitting material,writing can be performed with high energy efficiency.

The memory device and the semiconductor device of the present inventionare writable (additional writing) of data except in manufacturing tips.Furthermore, the memory device and the semiconductor device which canprevent forgery due to rewriting can be obtained since rewriting is notpossible. Further, the memory device and the semiconductor device have amemory element with a simple structure in which an organic compound issandwiched between a pair of conductive layers; thus a semiconductordevice can be is provided at low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C are cross-sectional views describing a memory element ofthis invention;

FIGS. 2A to 2C are cross-sectional views describing a memory element ofthis invention;

FIGS. 3A to 3C are cross-sectional views describing a memory element ofthis invention;

FIGS. 4A to 4C are cross-sectional views describing a memory element ofthis invention;

FIGS. 5A and 5B are cross-sectional views describing a memory element ofthis invention;

FIGS. 6A to 6C are cross-sectional views describing a memory element ofthis invention;

FIGS. 7A and 7B are cross-sectional views describing a memory element ofthis invention;

FIG. 8 is a cross-sectional view describing a memory element of thisinvention;

FIGS. 9A to 9C are cross-sectional views describing a memory element ofthis invention;

FIGS. 10A to 10C are cross-sectional views describing a memory elementof this invention;

FIGS. 11A to 11C are cross-sectional views describing a memory elementof this invention;

FIGS. 12A to 12C are cross-sectional views describing a memory elementof this invention;

FIGS. 13A to 13C are cross-sectional views describing a memory elementof this invention;

FIGS. 14A to 14C are views describing a memory device of this invention;

FIGS. 15A to 15D are a top view and cross sectional views of a memorydevice of this invention;

FIGS. 16A to 16C are views describing a memory device of this invention;

FIGS. 17A to 17C are a top view and cross sectional views of a memorydevice of this invention;

FIGS. 18A and 18B are cross sectional views describing a semiconductordevice of this invention;

FIGS. 19A and 19B are cross sectional views describing a semiconductordevice of this invention;

FIG. 20 is a cross sectional view describing a semiconductor device ofthis invention;

FIG. 21 is a view showing a current-voltage characteristic of a memoryelement and a resistance element;

FIGS. 22A to 22C are views describing a constitutional example of asemiconductor device of this invention;

FIG. 23 is a view describing an electric device having a semiconductordevice of this invention;

FIGS. 24A to 24F are views describing usage patterns of a semiconductordevice of this invention;

FIGS. 25A to 25D are cross sectional views describing a thin filmtransistor applicable to this invention;

FIGS. 26A to 26C are cross sectional views describing a light emittingelement applicable to this invention; and

FIG. 27A to 27C are cross sectional views describing a light emittingelement applicable to this invention.

DETAILED DESCRIPTION OF THE INVENTION Embodiment Mode

Hereinafter, embodiment modes of the invention are described withreference to the drawings. However, the present invention can be carriedout in many different modes, and it is easily understood by those ofordinary skill in the art that the modes and the detail of the inventioncan be changed variously unless otherwise such changes and modificationsdepart from the purpose and the scope of the present invention. Notethat the same symbol referring the same is commonly used in thedrawings.

In the embodiment modes, a structure of a memory element is describedusing a model diagram. Therefore, the size, the thickness and the shapeof each component of the memory element may be different from theoriginal.

Embodiment Mode 1

A structural example of a memory element included in a memory device ofthe invention is described with reference to drawings.

The memory element of this embodiment mode, as shown in FIGS. 1A to 1C,is formed of a first conductive layer 101, an organic compound layer 110having contact with the first conductive layer, and a second conductivelayer 103 having contact with the organic compound layer. The organiccompound layer 110 has a photosensitized oxidation reduction agent 106 awhich may come to an excited state by recombination energy of electronsand holes, and a substance 105 which may react by the photosensitizedoxidation reduction agent.

Current flows by raising electric potential of the first conductivelayer 101 than that of the second conductive layer 103, and holes andelectrons are recombined in the organic compound layer 110. Accordingly,the first conductive layer 101 serves as an anode and the secondconductive layer 103 serves as a cathode. In this embodiment mode,recombination of the holes and electrons in the photosensitizedoxidation reduction agent 106 a of the organic compound layer 110 isshown as an example.

As the first conductive layer 101, a material having a work function inthe range of 3.5 eV to 5.5 eV can be used. To be concrete, in additionto a transparent electrode such as indium tin oxide (ITO) and indium tinoxide added with silicon, titanium, molybdenum, tungsten, nickel, gold,platinum, silver, aluminum, and alloy thereof, and the like can be used.In particular, titanium, molybdenum, aluminum, or alloy thereof is amultipurpose metal used for a wiring, and a memory element can beprovided at low cost using it as the first conductive layer 101.

The organic compound layer 110 includes a substance 105 and aphotosensitized oxidation reduction agent 106 a.

As the photosensitized oxidation reduction agent 106 a, a alloxazineround or a compound such as chlorophyll which includes in a structure abasis having strong oxidation-reduction power in an excited state isgiven, and typically, lumichrome, alloxazine, lumiflavin, flavinmononucleotide, tetramethylene paraphenylene diamines, and the like aregiven. The photosensitized oxidation reduction agent 106 a comes to anoxidation agent or a reduction agent according to combination with thesubstance 105 and according to reaction condition.

The substance 105 is a compound which is decomposed or in whichstructural change occurs by photosensitized oxidation reductionreaction, to be more precise, by oxidation of alcohol, oxidativecleavage of alkene or the like, cyclization reaction, or ring-openingreaction, or the substance 105 is a compound from which de-doping of ametal can be performed by photosensitized oxidation reaction. As atypical compound which is decomposed or in which structural changeoccurs due to the photosensitized oxidation reduction reaction byoxidation of alcohol, oxidative cleavage of alkene and the like,cyclization reaction, or ring-opening reaction, an ascorbic acid,guanosine, dibenzofuran, 11-cis-3,4-didehydroretinal, an uridine athymidine or the like is given as an example.

The substance 105 is oxidized or reduced, according to a combinationwith a photosensitized oxidation reduction agent and according toreaction condition.

As a compound from which de-doping of a metal can be performed by aphotosensitized oxidation reduction reaction, fullerene, chlorophyll,phthalocyanine, haemin or the like each of which has a central metal canbe given as an example. As the central metal, aluminum (Al), titanium(Ti), chromium (Cr), vanadium (V), manganese (Mn), iron (Fe), cobalt(Co), nickel (Ni), copper (Cu), zinc (Zn), zirconium (Zr), niobium (Nb),molybdenum (Mo), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver(Ag), cadmium (Cd), indium (In), tin (Sn), cesium (Cs), hafnium (Hf),tantalum (Ta), tungsten (W), osmium (Os), iridium (Ir), platinum (Pt),gold (Au), lead (Pb), bismuth (Bi) or the like can be given.

The second conductive layer 103 can be formed of the same material asthe first conductive layer 101. Further, a metal with a low workfunction such as lithium, magnesium, calcium, barium, or alloy thereofcan be used for the second conductive layer 103.

Subsequently, writing of data of a memory element of this embodimentmode is described. As shown in FIG. 1A, voltage is applied to the firstconductive layer 101 and the second conductive layer 103 so as togenerate electric potential difference between the conductive layers.Accordingly, holes and electrons are recombined in the photosensitizedreducing agent 106 a of the layer 110 including an organic compound, andthe photosensitized reducing agent comes to an excited state 106 b asshown in FIG. 1B.

Then, at least one part of reaction in the substance 105 is promoted byexcited energy 100 a of the photosensitized oxidation reduction agent inthe excited state 106 b, and a product 107 is generated as shown in FIG.1C. As a typical example of the product, a material in which a substanceis decomposed, a material in which a structure of the substance ischanged, a material from which de-doping of a metal is performed, or thelike can be given. On the other hand, the photosensitized oxidationreduction agent in the excited state 106 b returns to thephotosensitized oxidation reduction agent 106 a before the excitedstate.

The product 107 of the substance 105 becomes an oxide when the substanceis oxidized, and becomes a reduced substance when the substance isreduced. The conductivity of the product 107 is different from that ofthe substance 105. Consequently, by applying voltage to the firstconductive layer and the second conductive layer, and generating theproduct 107, electric resistance of the memory element is changed.Typically, increase of the resistance which causes insulation, ordecrease of the resistance is given. Namely, voltage is applied to thefirst conductive layer 101 and the second conductive layer 103, thephotosensitized oxidation reduction agent in the organic compound layeris made an excited state, and oxidation reaction or reducing reaction ofthe substance is caused by the excited energy, thereby generating aproduct. The data can be written by the resulting change in the electricresistance of the memory element. Alternatively, there is a case whereheat is generated by the photosensitized oxidation reduction reaction ofthe substance, and the shape or the film thickness of the layer due tothe heat occur at the same time. Accordingly, data can be written in bythe change of the electric resistance of the memory element.

The data of the memory element can be read out by reading the differencebetween the electric resistance of the memory element before writing andthe electric resistance of the memory element after writing in.

In a memory device of this embodiment mode, a photosensitized oxidationreduction agent is excited by recombination energy of electrons andholes in the photosensitized oxidation reduction agent, and data iswritten in by generating photosensitized oxidation reduction reaction bythe excited energy and changing electric resistance of the memoryelement. At this time, a reaction product can be controlled. As aresult, variation of writing can be decreased and writing success can beincreased.

Embodiment Mode 2

In this embodiment mode, a memory element in which recombination ofholes and electrons are generated in a substance included in an organiccompound layer is described in comparison with Embodiment Mode 1 withreference to FIGS. 2A to 2C.

The memory element of this embodiment mode is formed of a firstconductive layer 101, an organic compound layer 110 having contact withthe first conductive layer, and a second conductive layer 103 havingcontact with the organic compound layer.

In this embodiment mode, the organic compound layer 110 includes asubstance 105 and a photosensitized oxidation reduction agent 106 a.Each of the first conductive layer 101, the second conductive layer 103,the substance 105, and the photosensitized oxidation reduction agent 106a can be formed of the same material as that in Embodiment Mode 1.

Then, writing of data of a memory element of this embodiment mode isdescribed. When voltage is applied to the first conductive layer 101 andthe second conductive layer 103 and potential difference is generatedbetween the both conductive layers as shown in FIG. 2A, holes andelectrons are recombined in the substance 105 of the organic compoundlayer 110, and recombination energy 100 b is generated.

The recombination energy is moved to the photosensitized oxidationreduction agent 106 a, and the photosensitized oxidation reduction agentcomes to an excited state 106 b as shown in FIG. 2B.

Then, at least one part of reaction in the substance 105 is promoted byexcited energy 100 a of the photosensitized oxidation reduction agent inan excited state 106 b, and a product 107 is generated as shown in FIG.2C. A typical example of the product is the same as the product 107 inEmbodiment Mode 1.

The conductivity of the product 107 of the substance 105 is differentfrom that one of the substance 108. Consequently, by applying voltage tothe first conductive layer and the second conductive layer, andgenerating the product 107, electric resistance of the memory element ischanged as in the case of Embodiment Mode 1. Typically, increase of theresistance which causes insulation, or decrease of the resistance isgiven. The data can be written by the resulting change in the electricresistance by the applied voltage to the first conductive layer 101 andthe second conductive layer 103.

The data of the memory element can be read out by reading the differencebetween the electric resistance of the memory element before writing inand the electric resistance of the memory element after writing in.

In the memory element of this embodiment mode, data is written in byexciting a photosensitized oxidation reduction agent by recombinationenergy of electrons and holes in the photosensitized oxidation reductionagent, and changing electric resistance of the memory element bygenerating photosensitized oxidation reduction reaction. At this time, areaction product can be controlled. As a result, variation in writingcan be decreased and writing success can be increased.

Embodiment Mode 3

In this embodiment mode, a structure of a memory element having a lightemitting material in an organic compound layer is described withreference to drawings in comparison with Embodiment Mode 1 andEmbodiment Mode 2.

The memory element of this embodiment mode is formed of a firstconductive layer 101, an organic compound layer 102 having contact withthe first conductive layer, and a second conductive layer 103 havingcontact with the organic compound layer.

In this embodiment mode, the organic compound layer 102 includes asubstance 105, a photosensitized oxidation reduction agent 106 a and alight emitting material 104. The first conductive layer 101, the secondconductive layer 103, the substance 105, and the photosensitizedoxidation reduction agent 106 a can be formed using the same material asthat in Embodiment Mode 1.

As the light emitting material 104, an organic compound havingpreferable energy transfer efficiency to the photosensitized oxidationreduction agent is used regardless of luminescence quantum efficiency.Therefore, one or more selected from a light emitting material, a holetransporting material, a hole injecting material, an electrontransporting material, and an electron injecting material can beproperly used. Here, the material with a high luminescence quantumefficiency is referred to as a light emitting material.

As the light emitting material, for example,9,10-di(2-naphthyl)anthracene (abbr.: DNA),2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbr.: t-BuDNA),4,4′-bis(2,2-diphenylvinyl) biphenyl (abbr.: DPVBi), Coumarin 30,Coumarin 6, Coumarin 545, Coumarin 545T, perylene, rubrene,periflanthene, 2,5,8,11-tetra(tert-butyl)perylene (abbr.: TBP),9,10-diphenylanthracene (abbr.: DPA), 5,12-diphenyltetracene,4-(dicyanomethylene)-2-methyl-6-[p-(dimethylamino)styryl]-4H-pyran(abbr.: DCM1),4-(dicyanomethylene)-2-methyl-6-[2-(joulolidine-9-yl)ethenyl]-4H-pyran(abbr.: DCM2),4-(dicyanomethylene)-2,6-bis[p-(dimethylamino)styryl]-4H-pyran (abbr.:BisDCM), or the like can be given. In addition, a compound which canemit phosphorescence can be used, such asbis[2-(4′,6′-difluorophenyl)pyridinato-N,C²](picolinato)iridium (abbr.:Flrpic), bis{2-[3′,5′-bis(trifluoromethyl)phenyl]pyridinato-N,C²}(picolinato)iridium(abbr.: Ir(CF₃ppy)₂(pic)), tris(2-phenylpyridinato-N,C²)iridium (abbr.:Ir(ppy)₃), (acetylacetonato)bis(2-phenylpyridinato-N,C²)iridium (abbr.:Ir(ppy)₂(acac)),(acetylacetonato)bis[2-(2′-thienyl)pyridinato-N,C³]iridium (abbr.:Ir(thp)₂(acac)), (acetylacetonato)bis(2-phenylquinolinato-N,C²)iridium(abbr.: Ir(pq)₂(acac)), or (acetylacetonato)bis[2-(2′-benzothienyl)pyridinato-N,C³]iridium (abbr.: Ir(btp)₂(acac)).

As the electron transporting material, tris(8-quinolinolato)aluminum(abbr.: Alq₃), tris(4-methyl-8-quinolinolato)aluminum (abbr.: Almq₃),bis(10-hydroxybenzo[h]-quinolinato) beryllium (abbr.: BeBq₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbr.: BAlq),bis[2-(2′-hydroxyphenyl)benzoxazolato]zinc (abbr.: Zn(BOX)₂),bis[2-(2′-hydroxyphenyl)benzothiazolato]zinc (abbr.: Zn(BTZ)₂),bathophenanthroline (abbr.: BPhen), bathocuproin (abbr.: BCP),2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbr.: PBD),1,3-bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene (abbr.:OXD-7), 2,2′,2″-(1,3,5-benzenetriyl)-tris(1-phenyl-1H-benzimidazole)(abbr.: TPBI),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (abbr.:TAZ),3-(4-biphenylyl)-4-(4-ethylphenyl)-5-(4-tert-butylphenyl)-1,2,4-triazole(abbr.: p-EtTAZ), or the like can be given; however, the electrontransporting material is not limited thereto.

As the electron injecting material, an ultrathin film of an insulator,for example, alkali metal halide such as LiF or CsF, alkaline earthmetal halide such as CaF₂, alkali metal oxide such as Li₂O, or the likeis often used besides the above-described electron transportingmaterial. Further, an alkali metal complex such as lithiumacetylacetonate (abbr.: Li(acac)) or 8-quinolinolato-lithium (abbr.:Liq) is also effective. Moreover, a material in which theabove-mentioned electron transporting material is mixed with metalhaving a low work function, such as Mg, Li, or Cs, by co-evaporation orthe like can also be used.

As the hole-transporting compound, for example, in addition tophthalocyanine (abbr.: H₂Pc), copper phthalocyanine (abbr.: CuPc), andvanadyl phthalocyanine (abbr.: VOPc), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine (abbr.: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (abbr.:MTDATA), 1,3,5-tris[N,N-di(m-tolyl)amino]benzene (abbr.: m-MTDAB),N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine(abbr.: TPD), 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbr.:NPB), 4,4′-bis{N-[4-di(m-tolyl)amino]phenyl-N-phenylamino}biphenyl(abbr.: DNTPD), 4,4′-bis[N-(4-biphenylyl)-N-phenylamino]biphenyl (abbr.:BBPB), 4,4′,4″-tri(N-carbazolyl)triphenylamine (abbr.: TCTA), or thelike can be used; however, it is not limited to these. Among theabove-mentioned compounds, an aromatic amine compound typified by TDATA,MTDATA, m-MTDAB, TPD, NPB, DNTPD, BBPB, TCTA, or the like easilygenerates holes, and is a compound group suitable for the organiccompound.

As the hole injecting material, phthalocyanine compounds are effective.For example, phthalocyanine (abbr.: H₂-Pc), copper phthalocyanine(abbr.: Cu-Pc), and vanadyl phthalocyanine (abbr.: VOPc), or the likecan be used. In addition, conductive high molecular compound compoundssubjected to chemical doping, such as dioxythiophene (abbr.: PEDOT)doped with polystyrene sulfonate (abbr.: PSS) and polyaniline (abbr.:PAni), can also be used. Further, a thin film of an inorganicsemiconductor such as molybdenum oxide (MoOx), vanadium oxide (VOx), ornickel oxide (NiOx) and an ultrathin film of an inorganic insulator suchas aluminum oxide (Al₂O₃) are also effective. In addition, aromaticamine compounds such as 4,4′,4″-tris(N,N-diphenyl-amino)-triphenylamine(abbr.: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenyl-amino]-triphenylamine (abbr.:MTDATA),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine(abbr.: TPD), 4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (abbr.:α-NPD), and 4,4′-bis[N-(4-(N,N-di-m-tolyl)amino)phenyl-N-phenylamino]biphenyl (abbr.: DNTPD)can also be used. Further, these hole transporting materials and holeinjecting materials may be doped with an acceptor substance. Forexample, VOPc doped with2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (abbr.: F₄-TCNQ)that is an acceptor and α-NPD doped with MoOx that is an acceptor may beused.

Subsequently, data writing of a memory element of this embodiment modeis described. As shown in FIG. 3A, by applying voltage to the firstconductive layer 101 and the second conductive layer 103 to generatepotential difference between the both conductive layers, holes andelectrons are recombined in the light emitting material 104 including anorganic compound layer.

When the recombination energy 100 b of the light emitting material movesto the photosensitized oxidation reduction agent 106 a, thephotosensitized oxidation reduction agent 106 a comes to an excitedstate 106 b and generates excitation energy.

Then, reaction of the substance 105 is promoted by the excitation energy100 a of the photosensitized oxidation reduction agent in the excitedstate 106 b, and at least one part of the product 107 of the substance105 is formed. As a typical example of the product, a material in whicha substance is decomposed, a material in which a substance isstructurally changed, a material in which de-doping of metal isperformed from a metal complex, or the like is given.

The conductivity of the product 107 of the substance 105 is differentfrom the conductivity of the substance 105. Therefore, electricresistance of the memory element is changed by applying voltage to thefirst conductive layer and the second conductive layer and generatingthe product 107. Typically, increase of the resistance which causesinsulation, or decrease of the resistance is given. Specifically,voltage is applied to the first conductive layer 101 and the secondconductive layer 103, electrons and holes are recombined in the lightemitting material and the recombination energy is transferred to thephotosensitized oxidation reduction agent. As a result, thephotosensitized oxidation reduction agent comes to an excited state, thesubstance is reacted by the excitation energy, electric resistance ofthe memory element is changed by forming the product, and data can bewritten in.

The data of the memory element can be read out by reading the differencebetween the electric resistance of the memory element before writing inand after writing in.

The memory element having a layer including the light emitting material,the photosensitized oxidation reduction agent, or the organic compoundhaving a substance can control the recombination of electrons and holesin the light emitting material. Thus, recombination probability of theholes and the electrons can be increased.

Embodiment Mode 4

In this embodiment mode, a memory element in which an organic compoundlayer has a first layer formed of a light emitting material and a secondlayer formed of a substance and a photosensitized oxidation reductionagent with reference to FIGS. 4A to 4C to FIGS. 7A and 7B, in comparisonwith Embodiment Mode 1.

The memory element of this embodiment mode is formed of a firstconductive layer 101, a first layer 111 having contact with the firstconductive layer, a second layer 112 having contact with the first layer111, and a second conductive layer 103 having contact with the secondlayer 112. Here, the first layer 111 is a layer formed of a lightemitting material 104, and the second layer 112 is a layer formed of asubstance 105 and a photosensitized oxidation reduction agent 106 a.Further, the first conductive layer 101, the second conductive layer103, the light emitting material 104, a substance 105, and thephotosensitized oxidation reduction agent 106 a are formed of the samematerial used in Embodiment Mode 1 to Embodiment Mode 3.

Here, the second layer 112 formed of the substance 105 and thephotosensitized oxidation reduction agent 106 a which are interposedbetween the first layer 111 formed of the light emitting material 104and the second conductive layer 103 functioning as a cathode. Therefore,the first layer 111 preferably functions as a hole transporting and/orinjecting layer, and the second layer preferably functions as anelectron transporting and/or injecting layer. Thus, in this embodimentmode, the light emitting material 104 is preferably formed of one ormore selected from the hole transporting materials and hole injectingmaterials shown in Embodiment Mode 3. The second layer functions as anelectron transporting layer and/or an electron injecting layer inaccordance with a mixture ratio of the photosensitized oxidationreduction agent and the substance.

Subsequently, data writing of a memory element of this embodiment modeis described. As shown in FIG. 4A, by applying voltage to the firstconductive layer 101 and the second conductive layer 103 to generatepotential difference between the both conductive layers, holes andelectrons are recombined in the first layer 111, and recombinationenergy 100 b is generated. By moving the recombination energy to thephotosensitized oxidation reduction agent 106 a, as shown in FIG. 4B,the photosensitized oxidation reduction agent 106 a comes to an excitedstate 106 b. Note that when holes and electrons are recombined and emitlight, the photosensitized oxidation reduction agent is irradiated withemission energy, and the photosensitized oxidation reduction agent 106 acomes to the excited state.

The reaction of the substance 105 is promoted by the excitation energy100 a of the photosensitized oxidation reduction agent in an excitedstate 106 b, and a product 107 is formed as shown in FIG. 4C.

The conductivity of the product 107 of the substance is different fromthe one of the substance 105. Consequently, by applying voltage to thefirst conductive layer 101 and the second conductive layer 103 togenerate the product 107, electric resistance of the memory element ischanged as in the case of Embodiment Mode 1. Typically, increase of theresistance which causes insulation, or decrease of the resistance isgiven. The data can be written by the resulting change in the electricresistance by the applied voltage to the first conductive layer 101 andthe second conductive layer 103.

The data of the memory element can be read out by reading the differencebetween the electric resistance of the memory element before writing inand after writing in.

As shown in FIG. 5A, an electron injecting layer 113 may be providedbetween the second conductive layer 103 and the second layer 112. Theelectron injecting layer 113 can be formed by using the above mentionedelectron injecting materials.

Furthermore, as shown in FIG. 5B, as the electron injecting layer 113 isprovided between the second conductive layer 103 and the second layer112, a hole injecting layer 115 and a hole transporting layer 114 may beprovided between the first conductive layer 101 and the first layer 111.The hole injecting layer 115 can be formed using the above mentionedhole injecting materials. The hole transporting layer 114 can be formedusing the above mentioned hole transporting material.

As shown in FIG. 6A, the memory element may be formed of the firstconductive layer 101, the first conductive layer 121 having contact withthe first conductive layer, the second layer 122 having contact with thefirst conductive layer 121, and the second conductive layer 103 havingcontact with the second layer 122. The second layer 122 is formed of thelight emitting material 104. The first conductive layer 101, the secondconductive layer 103, the light emitting material 104, the substance105, and the photosensitized oxidation reduction agent 106 a are formedusing the same materials described in Embodiment Mode 1 to EmbodimentMode 3.

Here, the first layer 121 formed of the substance 105 and thephotosensitized oxidation reduction agent 106 a is interposed betweenthe second layer 122 formed of the light emitting material 104 and thefirst conductive layer 101 functioning as an anode. Therefore, the firstlayer 121 preferably functions as a hole transporting and/or injectinglayer, and the second layer preferably functions as an electrontransporting and/or injecting layer. The light emitting material 104 ispreferably formed of the one or more selected from the electrontransporting materials and the electron injecting materials shown inEmbodiment Mode 3. Note that the first layer 121 may have a lightemitting material. The second layer 122 functions as a hole transportinglayer or a hole injecting layer in accordance with a mixture ratio ofthe photosensitized oxidation reduction agent to the substance.

As shown in FIG. 7A, a hole injecting layer 115 may be provided betweenthe first conductive layer 101 and the first layer 121. The holeinjecting layer 115 can be formed by properly using the hole injectingmaterials.

As shown in FIG. 7B, as the hole injecting layer 115 is provided betweenthe first conductive layer 101 and the first layer 121, an electrontransporting layer 123 and the electron injecting layer 113 may beprovided between the second conductive layer 103 and the second layer122. The electron injecting layer 113 can be formed by properly usingthe above mentioned electron injection materials. The electrontransporting layer 123 can be formed by properly using the abovementioned electron transporting materials.

A writing method and a reading method are similar to the memory elementshown in FIGS. 4A to 4C. To be concrete, as shown in FIG. 6A and FIG.7A, by applying voltage to the first conductive layer 101 and the secondconductive layer 103 to generate potential difference between theconductive layers, holes and electrons are recombined in the secondlayer 122. By moving the recombination energy to the photosensitizedoxidation reduction agent 106 a, the photosensitized oxidation reductionagent comes to an excited state 106 b as shown in FIG. 6B and FIG. 7A.Subsequently, reaction of the substance 105 is promoted by theexcitation energy of the photosensitized oxidation reduction agent inthe excited state 106 b, and a product 107 is generated as shown in FIG.6C and FIG. 7C.

The conductivity of the product 107 of the substance is different fromthe one of the substance 105. Consequently, by applying voltage to thefirst conductive layer 101 and the second conductive layer 103 togenerate the product 107, electric resistance of the memory element ischanged as in the case of Embodiment Mode 1. Typically, increase of theresistance which causes insulation, or decrease of the resistance isgiven. The data can be written in by the resulting change in theelectric resistance by the applied voltage to the first conductive layer101 and the second conductive layer 103.

The data of the memory element can be read out by reading the differencebetween the electric resistance of the memory element before writing inand after writing in.

As shown in FIG. 8, the memory element may be formed of the firstconductive layer 101, the hole injecting layer 115 having contact withthe first conductive layer, the first layer 121 having contact with thehole injecting layer 115, a second layer 124 having contact with thefirst layer 121, a third layer 125 having contact with the second layer124, the electron injecting layer 113 having contact with the thirdlayer, and the second conductive layer 103 having contact with theelectron injection layer 113. Here, the first layer 121 is a layerformed of the substance 105 and the photosensitized oxidation reductionagent 106 a, and functions as a hole transporting and/or injecting layerhere. The second layer 124 is a layer formed of the light emittingmaterial 104. The third layer 125 is a layer formed of the substance 105and the photosensitized reducing agent 106 a, and functions as anelectron transporting and/or injecting layer.

By laminating the layer formed of the light emitting material and thelayer having the substance and the photosensitized oxidation reductionagent as described in this embodiment mode, holes or electrons whichpass through the layer having the substance and the photosensitizedoxidation reduction agent without being recombined can be recombined inthe layer formed of the light emitting material. Therefore,recombination probability can be heightened, and accordingly, writing ofthe memory element can be performed easily.

Embodiment Mode 5

In this embodiment mode, a memory element in which a light emittingelement portion having an organic compound layer formed of a lightemitting material and a memory element portion having an organiccompound layer formed of a photosensitized oxidation reduction agent anda substance are connected with a light-transmitting conductive layerwhich is a common electrode is described with reference to FIGS. 10A to10C and FIGS. 11A to 11C. In this embodiment mode, one of the electrodesof the light emitting element portion and one of the electrodes of thememory element portion are to be a common electrode, and formed of amaterial having a light-transmitting property, therefore, thephotosensitized oxidation reduction agent in the memory element can beirradiated with light emitted from a light emitting element, and thephotosensitized oxidation reduction agent can be in an excited state.

The memory element of this embodiment mode is formed of a firstconductive layer 101, a first layer 142 having contact with the firstconductive layer, a conductive layer 141 having a light-transmittingproperty and having contact with the first layer 142, a second layer 143having contact with the conductive layer 141 having a light-transmittingproperty, and a second conductive layer 103 having contact with thesecond layer 143. Here, the first conductive layer 101, the first layer142 having contact with the first conductive layer, and the conductivelayer 141 having a light-transmitting property and having contact withthe first layer 142 function as a light emitting element portion, andthe conductive layer 141 having a light-transmitting property, thesecond layer 143 having a light-transmitting property and having contactwith the conductive layer 141, and the second conductive layer 103having contact with the second layer 143 each function as a memoryelement portion.

The first layer 142 of the light emitting element portion is a layerformed of a light emitting material 104. In particular, the first layer142 is preferably formed with a hole injection layer 142 a, a holetransporting layer 142 b, a light emitting layer 142 c, an electrontransporting layer 142 d, and an electron injecting layer 142 e. Byapplying such a structure, electrons and holes are recombined in thelight emitting layer 142 c when voltage is applied to the firstconductive layer 101 and the second conductive layer 103.

The second layer 143 is a layer formed with a substance 105 and aphotosensitized oxidation reduction agent 106 a.

The conductive layer 141 having a light-transmitting property is formedby properly using ITO, indium tin oxide including silicon, indium oxideincluding 2 to 20% of zinc oxide (ZnO), or the like. Furthermore,titanium, molybdenum, tungsten, nickel, gold, platinum, silver,aluminum, lithium, magnesium, calcium, barium, and alloy thereof, or thelike, each of which has a thin film thickness and which can transmitlight (typically 1 nm to 10 nm film thickness) can be used for formingthe conductive layer 141.

Subsequently, data writing of the memory element of this embodiment modeis described. As shown in FIG. 10A, by applying voltage to the firstconductive layer 101 and the conductive layer 141 having alight-transmitting property to generate potential difference between theconductive layers, holes and electrons are recombined in the first layer142, the light emitting material 104 emits light, and light energy 100 cis generated.

When the photosensitized oxidation reduction agent 106 a of the secondlayer 143 is irradiated with light emitted from the light emittingmaterial 104, A shown in FIG. 10B, the photosensitized oxidationreduction agent 106 a comes to an excited state 106 b by the lightenergy.

Then, reaction of the substance 105 is promoted by excitation energy 100a of the photosensitized oxidation reduction agent in the excited state106 b, and a product 107 is generated as shown in FIG. 10C.

The conductivity of the product 107 of the substance is different fromthe one of the substance 105. Therefore, electric resistance of thememory element is changed similarly to Embodiment Mode 1 by applyingvoltage to the first conductive layer 101 and the second conductivelayer 103 to generate the product 107. Typically, increase of theresistance which causes insulation, decrease of the resistance or thelike is given. Therefore, data can be written in by the change of theelectric resistance due to the applied voltage to the first conductivelayer 101, the conductive layer 141 having a light-transmittingproperty, and the second conductive layer 103.

Note that data of the memory element can be read out by reading out thedifference between the electric resistance of the memory element beforewriting in and the electric resistance of the memory element afterwriting in.

As shown in FIG. 11A, the memory element can be formed of the firstconductive layer 101, the first layer 144 having contact with the firstconductive layer, the conductive layer 141 having a light-transmittingproperty and having contact with the first layer 144, the second layer145 having a light-transmitting property and having contact with theconductive layer 141, and the second conductive layer 103 having contactwith the second layer 145.

Here, the first conductive layer 101, the first layer 144 having contactwith the first conductive layer, and the conductive layer 141 havingcontact with the first layer 144 and having a light-transmittingproperty function as a memory element portion, and the conductive layer141 having a light-transmitting property, the second layer 145 having alight-transmitting property and having contact with the conductive layer141, and the second conductive layer 103 having contact with the secondlayer 145 function as a light emitting element portion. Further, voltageis applied only to the second conductive layer 103 and the conductivelayer 141 having a light-transmitting property.

The first layer 144 is a layer formed of the substance 105 and thephotosensitized oxidation reduction agent 106 a.

The first layer 145 which is one part of the light emitting element is alayer formed of a light emitting material 104. To be concrete, it ispreferably formed of a hole injecting layer 145 a, a hole transportinglayer 145 b, a light emitting layer 145 c, an electron transportinglayer 145 d and an electron injecting layer 145 e. By employing such astructure, recombination of electrons and holes are generated in thelight emitting layer 145 c when voltage is applied to the firstconductive layer and the second conductive layer.

The writing method and the reading method are similar to the memoryelement shown in FIGS. 10A to 10C. To be concrete, as shown in FIG. 11A,by applying voltage to the first conductive layer 101, the conductivelayer 141 having a light-transmitting property, and the secondconductive layer 103 to generate potential difference between theconductive layers, holes and electrons are recombined in the secondlayer 145, the light emitting material 104 emits light, and light energy100 c is generated.

When the photosensitized oxidation reduction agent 106 a of the firstlayer 144 is irradiated with the light emitted from the light emittingmaterial 104, the photosensitized oxidation reduction agent 106 a comesto an excited state 106 b as shown in FIG. 11B.

Then, reaction of the substance 105 is promoted by the excitation energy100 a of the photosensitized oxidation reduction agent in the excitedstate 106 b, and a product 107 is formed as shown in FIG. 11C.

The conductivity of the product 107 of the substance is different fromthe one of the substance 105. Therefore, electric resistance of thememory element is changed by applying voltage to the first conductivelayer 101 and the second conductive layer 103 to generate the product107. Typically, increase of the resistance which causes insulation, ordecrease of the resistance is given. Therefore, data can be written inby the change of the electric resistance due to the applied voltage tothe first conductive layer 101, conductive layer 141 having alight-transmitting property, and the second conductive layer 103.

Note that data of the memory element can be read out by reading thedifference between the electric resistance of the memory element beforebeing writing in and the electric resistance of the memory element afterwriting in.

In the memory element of this embodiment mode, a light emitting elementportion having an organic compound layer formed of a light emittingmaterial and a memory element portion having an organic compound layerformed of a photosensitized oxidation reduction agent and a substanceare connected with a conductive layer having a light-transmittingproperty which is a common electrode. Therefore, voltage can be appliedto each of the light emitting portion and the memory element portion.Here, since voltage that is enough for light emission in the lightemitting element portion is applied, energy can be easily generated whenholes and electrons are recombined. Furthermore, a photosensitizedoxidation reduction agent and a substance are not included in the lightemitting element portion. Thus, data writing into the memory element canbe performed at low voltage compared to the case in Embodiment Mode 4.Furthermore, since a memory element itself emits light and data can bewritten using the emitted light without providing a light irradiationdevice to perform writing outside, miniaturization and high integrationof a memory device and a semiconductor device are possible.

Embodiment Mode 6

In this embodiment mode, the second layer 143 formed of the substance105 and the photosensitized oxidation reduction agent 106 a shown inEmbodiment Mode 5 and FIGS. 10A to 10C, and the first layer 144 formedof the substance 105 and the photosensitized oxidation reduction agent106 a shown in Embodiment Mode 5 and FIGS. 11A to 11C have a lightemitting material.

The memory element of this embodiment mode is formed of a firstconductive layer 101, a first layer 142 having contact with the firstconductive layer 101, a conductive layer 141 having contact with thefirst layer 142 and having a light-transmitting property, a second layer146 having a light-transmitting property and having contact with theconductive layer 141, and a second conductive layer 103 having contactwith the second layer 146. Here, the first layer 142 is a layer formedof a light emitting material 104, and the second layer 143 is a layerformed of a substance 105, a photosensitized oxidation reduction agent106, and a light emitting material 147.

The first layer 142 is a layer formed of a light emitting material 104and has the same structure as that of FIGS. 12A to 12C.

Subsequently, data writing of a memory element of this embodiment modeis described. As shown in FIG. 12A, by applying voltage to the firstconductive layer 101, the conductive layer 141 having alight-transmitting property and the second conductive layer 103 togenerate potential difference between the first conductive layer 101 andthe conductive layer 141 having a light-transmitting property andbetween the conductive layer 141 having a light-transmitting propertyand the second conductive layer 103, holes and electrons are recombinedin the light emitting material 104 of the first layer 142, the lightemitting material 104 emits light, and holes and electrons are alsorecombined and emit light in the light emitting material 147 of thesecond layer 148 at the same time, thereby generating light energy 100c.

When the photosensitized oxidation reduction agent 106 a of the secondlayer 146 is irradiated with light emitted from the light emittingmaterials 104 and 147, as shown in FIG. 12B, the photosensitizedoxidation reduction agent 106 a come to an excited state 106 b and hasexcitation energy 100 a. When the light emitting material 147 comes intocontact with the photosensitized oxidation reduction agent 106 a,recombination energy moves to the photosensitized oxidation reductionagent 106 a even if the light emitting material 147 does not emit light.

Then, reaction of the substance 105 is promoted by the excitation energy100 a of the photosensitized oxidation reduction agent in an excitedstate 106 b, and a product 107 is formed as shown in FIG. 12C.

The conductivity of the product 107 of the substance is different fromthat of the substance 105. Therefore, electric resistance of the memoryelement is changed by applying voltage to the first conductive layer 101and the second conductive layer 103 to generate the product 107 in asimilar manner to that in Embodiment Mode 1. Typically, increase of theresistance which causes insulation, or decrease of the resistance isgiven. Therefore, data can be written in by the change of the electricresistance due to the applied voltage to the first conductive layer 101,the conductive layer 141 having a light-transmitting property, and thesecond conductive layer 103.

Note that data of the memory element can be read out by reading thedifference in the electric resistance of each memory element.

As shown in FIG. 13A, the memory element may be formed of the firstconductive layer 101, a first layer 148 having contact with the firstconductive layer 101, the conductive layer 141 having alight-transmitting property and having contact with the first layer 148,a second layer 145 having a light-transmitting property and havingcontact with the conductive layer 141, and the second conductive layer103 having contact with the second layer 145. Here, the first layer 148is a layer formed of a substance 105, a photosensitized oxidationreduction agent 106 a, and a light emitting material 149. Furthermore, asecond layer 145 is a layer formed of the light emitting material 104.

The writing method and the reading method are similar to the memoryelement shown in FIGS. 12A to 12C. To be concrete, as shown in FIG. 13A,by applying voltage to the first conductive layer 101, the conductivelayer 141 having a light-transmitting property, and the secondconductive layer 103 to generate potential difference between the firstconductive layer 101 and the conductive layer 141 having alight-transmitting property and between the conductive layer 141 havinga light-transmitting property and the second conductive layer 103, holesand electrons are recombined in the light emitting material 104 of thesecond layer 145, the light emitting material 104 emits light, holes andelectrons are also recombined in the light emitting material 147 of thefirst layer 148 and emit light, and light energy 100 c is generated.

When the photosensitized oxidation reduction agent 106 a of the firstlayer 148 is irradiated with light emitted from the light emittingmaterials 104 and 147, as shown in FIG. 13B, the photosensitizedoxidation reduction agent 106 a comes to an excited state 106 b and hasexcitation energy 100 a. When the light emitting material 147 comes intocontact with the photosensitized oxidation reduction agent 106 a,recombination energy moves to the photosensitized oxidation reductionagent 106 a even if the light emitting material 147 does not emit light.

Then, reaction of the substance 105 is promoted by the excitation energyof the photosensitized oxidation reduction agent in an excited state 106b, and a product 107 is formed as shown in FIG. 13C.

The conductivity of the product 107 of the substance is different fromthe one of the substance 105. Therefore, electric resistance of thememory element is changed by applying voltage to the first conductivelayer and the second conductive layer to generate the product 107 asshown in Embodiment Mode 1. Typically, increase of the resistance whichcauses insulation, or decrease of the resistance is given. Therefore,data can be written in by the change of the electric resistance due tothe applied voltage to the first conductive layer 101, the conductivelayer 141 having a light-transmitting property, and the secondconductive layer 103.

Note that data of the memory element can be read out by reading thedifference in the electric resistance of each memory element.

In the memory element of this embodiment mode, a light emitting elementportion having an organic compound layer formed of a light emittingmaterial and a memory element portion having an organic compound layerformed of a photosensitized oxidation reduction agent and a substanceare connected with a conductive layer having a light-transmittingproperty which is a common electrode. Furthermore, the layer formed ofthe substance and the photosensitized oxidation reduction agent in thememory element portion includes a light emitting material, andrecombination energy generated by the recombination of the lightemitting material in the layer moves to the photosensitized oxidationreduction agent 106 a. Therefore, the photosensitized oxidationreduction agent can come to an excited state by even more recombinationenergy. As a result, data writing at low voltage is possible and writingsuccess can be heightened. Moreover, the memory element itself emitslight and data can be written in using the light without providing alight irradiation device outside, and therefore, miniaturization andintegration of the memory device and the semiconductor device can beobtained.

Embodiment Mode 7

In the memory element shown in Embodiment Modes 1 to 6, a chargetransport layer formed of an inorganic compound and an organic compoundmay be provided between a first conductive layer and an organic compoundlayer. A charge transport layer formed of an inorganic compound and anorganic compound may be provided between a second conductive layer andan organic compound layer. Furthermore, a charge transport layer formedof an inorganic compound and an organic compound may be provided betweenthe first conductive layer and the organic compound layer and betweenthe second conductive layer and the organic compound layer,respectively. Note that description of this embodiment mode is providedwith reference to Embodiment Mode 1; however, the embodiment mode canalso adapt to Embodiment Mode 2 to Embodiment Mode 6.

In the memory element shown in FIG. 9A, a hole transporting layer 151 isincluded between a first conductive layer 101 functioning as an anodeand an organic compound layer 102. The hole transporting layer 151 has astructure including an organic compound and an inorganic compound havingan electron-accepting property with respect to the organic compound. Bymixing the inorganic compound having the electron-accepting property tothe organic compound, a large number of holes are generated in theorganic compound and excellent hole injecting and/or transportingproperties can be given.

Since holes are generated in the organic compound, as the organiccompound, the above mentioned organic compound having a holetransporting property is properly used to form the organic compound. Asthe inorganic compound, anything which can easily receive electrons fromthe organic compound is fine to be used. For example, various metaloxides and metal nitrides can be used, however, any transition metaloxide belonging group 4 to group 12 of the periodic table easily giveselectron-accepting property, and are preferable. To be concrete,titanium oxide, zirconium oxide, vanadium oxide, molybdenum oxide,tungsten oxide, rhenium oxide, ruthenium oxide, zinc oxide and the likeare given as examples. In the above mentioned metal oxides, anytransition metal oxide belonging to group 4 to group 8 of the periodictable has higher electron-accepting property and are particularlypreferable. In particular, vanadium oxide, tungsten oxide, and rheniumoxide are preferable since vacuum deposition is applicable and they areeasy to handle.

The memory element shown in FIG. 9B has an electron transporting layer152 between a second conductive layer 103 functioning as a cathode andthe organic compound layer 102. The electron transporting layer 152 hasa structure including an organic compound and an inorganic compoundhaving an electron donating property as against the organic compound. Bymixing the inorganic compound having the electron donating property withrespect to the organic compound, a large number of electrons aregenerated in the organic compound and excellent electron injectingand/or transporting properties can be given.

Since electrons are generated in the organic compound, the abovementioned organic compounds having the electron transporting propertyare properly used for the organic compound. Furthermore, as theinorganic compound, anything which can easily provide electrons from theorganic compound is fine to be used, and various metal oxides or metalnitrides can be used. An alkali metal oxide, an alkaline earth metaloxide, a rare-earth metal oxide, an alkali metal nitride, an alkalineearth metal nitride, and a rare-earth metal nitride are preferably usedsince each of which gives electron-donating ability. To be concrete,lithium oxide, strontium oxide, barium oxide, erbium oxide, lithiumnitride, magnesium nitride, calcium nitride, yttrium fluoride, andlanthanum nitride are given as examples. Since lithium oxide, bariumoxide, erbium oxide, lithium nitride, magnesium nitride, and magnesiumnitride can use vacuum evaporation and are easy to handle, they arepreferably used.

The memory element shown in FIG. 9C includes a hole transporting layer151 between a first conductive layer 101 functioning as an anode and anorganic compound layer 102, and an electron transporting layer 152between a second conductive layer 103 functioning as a cathode and theorganic compound layer 102.

Note that a hole transporting layer may be additionally formed using theabove mentioned organic compounds having a hole transporting propertybetween the hole transporting layer 151 and the organic compound layer102. Furthermore, an electron transporting layer may be formed using theabove mentioned organic compounds having an electron transportingproperty between the electron transporting layer 152 and the organiccompound layer 102.

As described, excellent conductivity can be also obtained in the memoryelement by providing the charge transport layer formed using the organiccompound and the inorganic compound between the conductive layer and theorganic compound layer. Therefore, electrons and holes can be recombinedat lower voltage than ever before, and data writing can be performed atlow power consumption.

Embodiment Mode 8

In this embodiment mode, a structural example of a memory device havinga memory element in the above mentioned embodiment modes is describedwith reference to drawings. To be concrete, the case where the structureof the memory device is a passive matrix type is described.

FIG. 14A shows one structural example of a memory device of thisembodiment mode. The memory device includes a memory cell array 22 inwhich memory cells 21 are arranged in a matrix form, a bit line drivercircuit 26 having a column decoder 26 a, a readout circuit 26 b, and aselector 26 c, a word line driver circuit 24 having a row decoder 24 aand a level shifter 24 b, and an interface 23 having a write circuit andthe like and communicating with an external portion. Note that thestructure of the memory device 16 shown in FIG. 14A is just one example;and therefore, the memory device may further include other circuits suchas a sense amplifier, an output circuit, and a buffer, or, a writecircuit may be provided in the bit line driver circuit.

Each of the memory cells 21 has a first conductive layer constituting abit line Bx (1≦x≦m), a second conductive layer constituting a word lineWy (1≦y≦n), and an organic compound layer. The organic compound layer isprovided between the first conductive layer and the second conductivelayer and includes a singe layer or a plurality of layers.

Examples of a top structure and cross-sectional structures of the memorycell array 22 are shown in FIGS. 15A to 15D. FIG. 15A shows a topstructure of the memory cell array 22, FIG. 15B and FIG. 15C show crosssectional structures along a line A-B of FIG. 15A, and FIG. 15D shows across sectional structure along a line C-D of FIG. 15A. Note that aninsulating layer 27 functioning as a protection film is not shown inFIG. 15A.

In the memory cell array 22, the memory cells 21 are provided in amatrix form (see FIG. 15A). Each of the memory cells 21 has a memoryelement 80 (see FIG. 15B). Over a substrate 30, the memory element 80includes a first conductive layer 31 extending in a first direction, anorganic compound layer 29 covering the first conductive layer 31, and asecond conductive layer 28 extending in a second direction orthogonal tothe first direction. Further, here, an insulating film 27 functioning asa protection film is formed to cover the second conductive layer 28.

The memory elements shown in Embodiment Mode 1 to 7 can be properly usedas the memory element 80.

In the above memory element, an element having a rectifying property maybe provided at the opposite side of the organic compound layer 29through the first conductive layers 31. The element having therectifying property is a transistor whose gate electrode and drainelectrode are connected to each other, a diode, or the like. As atypical diode, a PN junction diode, a PIN junction diode, an avalanchediode, and the like can be given. Alternatively a diode having anotherstructure may be used. Note that an element having a rectifying propertymay be provided at the opposite side of the organic compound layerthrough the second conductive layer. An element having a rectifyingproperty may be provided between the organic compound layer 29 and thefirst conductive layers 31. Also, an element having a rectifyingproperty may be provided between the organic compound layer 29 and thesecond conductive layer 28. By providing an element having a rectifyingproperty in such a manner, current only flows in one direction, andtherefore, readout errors are reduced and a readout margin is improved.

Further, a thin film transistor (TFT) may be provided over a substratehaving an insulating property and a memory element 80 may be providedthereover. As a substitute for the substrate having the insulatingproperty, a field-effect transistor (FET) may be formed over asemiconductor substrate such as a Si substrate or an SOI substrate, andthe memory element 80 may be provided thereover. Furthermore, since thetransistor formed of a single crystal semiconductor can bemicrofabricated, high integration and miniaturization of a semiconductordevice are possible. Furthermore, since the transistor formed of asingle crystal semiconductor can be microfabricated, high integrationand miniaturization of a semiconductor device are possible. Moreover,since the transistor is formed of the single crystal semiconductor,high-speed operation is possible. Note that examples in which the memoryelement is formed over the thin film transistor or the field effecttransistor are shown here; however, the memory element may be attachedto the thin in different steps from each other, and then the memoryelement and the thin film transistor or the field-effect transistor areattached to each other by using a conductive film, an anisotropicconductive adhesive agent, or the like. Furthermore, any known structuremay be used for the thin film transistor or the field-effect transistor.

When there is a concern that an adverse effect of an electric field iscaused in a horizontal direction between adjacent memory elements,partition walls (insulating layers) may be provided between the organiccompound layers provided in each of memory elements so as to isolate theorganic compound layers provided in each of the memory elements from oneanother. Alternatively, the organic compound layer may be selectivelyprovided in each memory cell.

When an organic compound layer 29 is provided so as to cover the firstconductive layers 31, partition walls (insulating layers) 39 may beprovided so as to prevent a disconnection of the organic compound layer29 caused by steps of the first conductive layers 31 or an adverseeffect of an electric field in the horizontal direction between adjacentmemory cells (FIG. 15C). Note that in cross sections of the partitionwalls (insulating layers) 39, a side surface of each of the partitionwalls (insulating layers) 39 preferably has an angle of gradient of 10degrees or more and less than 60 degrees, and more preferably, 25degrees or more and 45 degrees or less with respect to the surfaces ofthe first conductive layers 31. Furthermore, the partition walls(insulating layers) 39 preferably have a curved shape. Thereafter, theinsulating layers 32, the organic compound layer 29, and the secondconductive layer 28 are provided so as to cover the first conductivelayers 31 and the partition walls (insulating layers) 39.

In place of the partition walls (insulating layers) 39, an interlayerinsulating layer 40 a partly covering the first conductive layer 31extending in the first direction may be provided over the substrate 30,and partition walls (insulating layers) 40 b may be provided over theinterlayer insulating layers (FIG. 15D).

The interlayer insulating layers 40 a partly covering the firstconductive layer 31 has an opening for each memory element 80. Thepartition walls (insulating layers) 40 b are provided in regions wherethe opening is not provided in the interlayer insulating layers. Thepartition walls (insulating layers) 40 b extend in the second directionin a similar manner to the second conductive layers 28. Further, a crosssection of each of the partition walls (insulating layers) 40 b has anangle of gradient of 95 degrees or more and 135 degrees or less withrespect to a surface of each of the interlayer insulating layers 40 a.

The partition walls (insulating layers) 40 b are formed byphotolithography, wherein a positive photosensitive resin in which a nonexposure portion remains, is used, and light exposure or developing timeis controlled such that a lower portion of a pattern is etched more. Theheight of the partition walls (insulating layers) 40 b is set largerthan the thickness of the organic compound layer 29 and the secondconductive layers 28. As a result, the organic compound layers 29 andthe second conductive layers 28 can be formed in a striped-form, whichare electrically isolated from one another in a plurality of regions andextend in a direction intersect with the first direction of the firstconductive layers 31, only by a process of evaporating the organiccompound layers 29 and the second conductive layers 28 over an entiresurface of the substrate 30. Therefore, the number of steps can bereduced. Note that organic compound layers 29 a and conductive layers 28a are also provided over the partition walls (insulating layers) 40 b;however, they are not connected to the organic compound layers 29 andthe conductive layers 28.

An operation in writing data in a memory device will be described below.Here, a case where operation in writing data is performed by applyingvoltage is described (see FIGS. 14A to 14C and FIGS. 15A to 15D).

When data is written in the memory element by applying voltage, onememory cell 21 is selected by a row decoder 24 a, a column decoder 26 a,and a selector 26 c, and then, data is written in the memory cell 21 byusing a write circuit (see FIG. 14A). When voltage is applied betweenthe first conductive layer 31 and the second conductive layer 28 of thememory cell 21, a layer formed of a light emitting material emits light.An oxidation reduction agent in the organic compound layer comes to anexcited state by the light emitting energy. Moreover, the substancebrings about chemical reactions by the excited photosensitized oxidationreduction agent, and chemical reactants are generated. As a result,electric resistance of the memory element is changed.

As compared to other memory elements before writing in, electricresistance of the memory element having the chemical reactants islargely changed. By applying voltage to the memory cell, data is writtenin the memory cell by utilizing a change in electric resistance betweentwo conductive layers. For example, when data “1” is written in, in thecase where the memory cell is in the state of data “0”, resistance ischanged by selectively applying large voltage to the organic compoundlayer of a desired memory element.

Next, an operation in reading out data from an organic memory will bedescribed (see FIG. 14B). Data readout is performed by utilizing adifference in electric characteristics between the first and secondconductive layers included in a memory cell having the data “0” and amemory cell having the data “1”. For example, a method for reading outdata by utilizing a difference in electric resistance in a case whereeffective electric resistance between the first and second conductivelayers included in the memory cell having the data “0” (hereinafter,simply referred to as electric resistance of the memory cell) is R0 at areadout voltage and electric resistance of the memory cell having data“1” is R1 at a readout voltage, will be described. Note that R1<R0.Here, the readout circuit 26 b has a structure including a resistanceelement 46 and a sense amplifier 47, the resistance element 46 hasresistance value Rr, wherein R1<Rr<R0. However, as the structure of thereadout circuit 26 b, is not limited to the foregoing structures, andmay have any kind of structure. For example, a transistor 48 may be usedas a substitute for the resistance element 46, or a clocked inverter 49may be used as a substitute for the sense amplifier 47 (FIG. 14C). Asignal φ or an inversion signal φ, which becomes Hi in a case of readingout data and Lo in a case of reading out no data, is input in theclocked inverter 49.

When reading out data, the memory cell 21 is selected by the row decoder24 a, a column decoder 26 a, and the selector 26 c. Specifically,predetermined voltage Vy is applied to a word line Wy connected to thememory cell 21 by the row decoder 24 a. Further, a bit line Bx connectedto the memory cell 21 is connected to a terminal P of the readoutcircuit 26 b by the column decoder 26 a and the selector 26 c. As aresult, potential Vp of the terminal P becomes a value determined byresistance division generated by the resistance element 46 (resistancevalue Rr) and the memory cell 21 (resistance value R0 or R1).Accordingly, when the memory cell 21 has the data “0”,Vp0=Vy+(V0−Vy)×R0/(R0+Rr). Further, when the memory cell 21 has the data“1”, Vp1=Vy+(V0−Vy)×R1/(R1+Rr). As a result, by selecting Vref to bebetween Vp0 and Vp1 in FIG. 14A and by selecting a variation point ofthe clocked inverter between Vp0 and Vp1 in FIG. 14B, Lo/Hi (or Hi/Lo)is output as output voltage Vout in accordance with the data “0” anddata “1”, and reading out can be carried out.

For example, the sense amplifier 47 is operated with Vdd=3 V, and Vy=0V; V0=3 V; and Vref=1.5 V. If R0/Rr=Rr/R1=9, when the memory cell hasthe data “0”, Vp0 becomes 2.7 V and Hi is output as Vout. When thememory cell has the data “1”, Vp1 becomes 0.3 V and Lo is output asVout. Thus, data can be read out from the memory cell.

When reading out data, forward voltage is applied to the memory cell.Alternatively, reverse voltage may be applied thereto.

According to the above described method, a condition of electricresistance of the organic compound layer 29 is read out by a voltagevalue utilizing a difference in resistance values and resistancedivision. Of course, the readout method is not limited thereto. Forexample, the condition of electric resistance of the organic compoundlayer may be read out by comparing current values. Namely, the conditionof the electric resistance is read out by, for example, utilizing acurrent value Ia1 where voltage is not applied to an organic compoundlayer and a resistance value Ib1 where short-circuiting between twoconductive films is caused due to applied voltage, which satisfiesIa1<Ib1.

In this embodiment mode, the resistance value is read out bysubstituting it with the value of voltage; however, the presentinvention is not limited thereto. For example, the data may be read outby utilizing a difference in a current value other than to utilize adifference in electric resistance. Further, when an electroniccharacteristic of a memory cell has a diode characteristic in whichthreshold voltage is different between the data “0” and the data “1”,the condition of electric resistance of the organic compound layer maybe read out by utilizing a difference in threshold voltage. Furthermore,a method by which a bit line is pre-charged can be employed.

Embodiment Mode 9

In this embodiment mode, a memory device having a different structurefrom those of Embodiment Mode 8 will be described. Specifically, thememory device has an active matrix type structure.

FIG. 16A shows a structural example of a memory device shown in thisembodiment mode. The memory device includes a memory cell array 222 inwhich memory cells 221 are arranged in a matrix form, a bit line drivercircuit 226 having a column decoder 226 a, a readout circuit 226 b, anda selector 226 c, a word line driver circuit 224 having a row decoder224 a and a level shifter 224 b, and an interface 223 having a writecircuit and the like and communicating with an external portion. Notethat the structure of the memory device 216 shown here is just oneexample; and therefore, the memory device may further include othercircuits such as a sense amplifier, an output circuit, and a buffer, or,a write circuit may be provided in the bit line driver circuit.

Each of the memory cells 221 has a first wiring constituting a bit lineBx (1≦x≦m), a second wiring constituting a word line Wy (1≦y≦n), atransistor 240, and a memory element 241. The memory element 241 has astructure in which an organic compound layer is interposed between apair of conductive layers.

Next, examples of a top view and cross sectional views of the memorycell array 222 having the above mentioned structure will be describedwith reference to FIGS. 17A to 17C. FIG. 17A is a top view of the memorycell array 222. FIG. 17B is a cross sectional view along a line A-B ofFIG. 17A. In FIG. 17A, partition walls (insulating layers) 249, anorganic compound layer 244, and a second conductive layer 245, which areformed over first conductive layers 243, are omitted.

In the memory cell array 222, a plurality of memory cells 221 areprovided in a matrix form. Each of the memory cells 221 has a transistor240 serving as a switching element and a memory element 241 connected tothe transistor 240 over a substrate 230 having an insulated surface (seeFIGS. 17A and 17B). The memory element 241 has first conductive layers243 formed over an insulating layer 248, an organic compound layer 244covering the first conductive layers 243 and the partition walls(insulating layers) 249, and a second conductive layer 245. Note thatpartition walls (insulating layers) 249 covering a part of the firstconductive layers are formed. As the transistor 240, a thin filmtransistor is used. The memory cell array 222 further includes aninsulating layer 236 serving as a protection film so as to cover thesecond conductive layer 245.

One mode of a thin film transistor, which can be used for the transistor240, will be described with reference to FIGS. 25A to 25D. FIG. 25Ashows an example of a top gate type thin film transistor. An insulatinglayer 205 is provided over a substrate 230 having an insulated surface,and a thin film transistor is provided over the insulating layer 205.The thin film transistor includes a semiconductor layer 1302 and aninsulating layer 1303 serving as a gate insulating layer, over theinsulating layer 205. Over the insulating layer 1303, a gate electrode1304 is provided corresponding to the semiconductor film 1302. Over thegate electrode 1304, an insulating layer 1305 serving as a protectionlayer and an insulating layer 248 serving as an interlayer insulatinglayer are provided. First conductive layers 243 connected to a sourceregion and a drain region of the semiconductor layer are formed. Inaddition, an insulating layer serving as a protection layer may beprovided over the first conductive layers 243.

The semiconductor layer 1302 is formed by a semiconductor having acrystalline structure, and can be formed using an amorphoussemiconductor or a single crystalline semiconductor. In particular, acrystalline semiconductor formed by crystallizing an amorphous ormicrocrystalline semiconductor by laser irradiation, a crystallinesemiconductor formed by crystallizing an amorphous or microcrystallinesemiconductor by heat treatment, a crystalline semiconductor formed bycrystallizing an amorphous or microcrystalline semiconductor by heattreatment and laser irradiation, or the like is preferable to be used.In the heat treatment, a crystallization method using a metal elementsuch as nickel, which has a function of promoting crystallization of asilicon semiconductor, can be employed.

In the case of crystallizing by irradiating with laser light, it ispossible to conduct crystallization in such a way that a portion in acrystalline semiconductor that is melted by irradiation with laser lightis continuously moved in a direction where the laser light is delivered,wherein the laser light is continuous wave laser light or ultrashortpulsed laser light having a high repetition rate of 10 MHz or more and apulse width of 1 nanosecond or less, preferably 1 to 100 picoseconds. Byusing such a crystallization method, a crystalline semiconductor havinga large grain diameter with a crystal grain boundary extending in onedirection can be obtained. By making a drift direction of carriersconform to the direction where the crystal grain boundary extends, theelectric field effect mobility in the transistor can be increased. Forexample, 400 cm²/V sec or more can be achieved.

In the case of applying the above crystallization step to acrystallization process where the temperature is not more than the uppertemperature limit of a glass substrate (approximately 600° C.), a largeglass substrate can be used. Therefore, a large number of semiconductordevices can be manufactured with one substrate, and cost can bedecreased.

The semiconductor layer 1302 may be formed by conducting acrystallization step through heating at the temperature higher than theupper temperature limit of a glass substrate. Typically, a quartzsubstrate is used as the insulating substrate and an amorphous ormicrocrystalline semiconductor is heated at 700° C. or more to form thesemiconductor layer 1302. As a result, a semiconductor with superiorcrystallinity can be formed. Therefore, a thin film transistor which issuperior in response speed, mobility, and the like and which is capableof high-speed operation can be provided.

The gate electrode 1304 can be formed using metal or a polycrystallinesemiconductor added with an impurity having one conductivity type. Whenthe gate electrode 1304 is formed using metal, tungsten (W), molybdenum(Mo), titanium (Ti), tantalum (Ta), aluminum (Al), or the like can beused. In addition, metal nitride formed by nitriding the above mentionedmetal, can be used. Further, the gate electrode 1304 may include a firstlayer made from the metal nitride and a second layer made from themetal. In the case where the gate electrode 1304 has a laminatedstructure, an edge of the first layer may protrude from an edge of thesecond layer. In this case, when the first layer is formed using metalnitride, the first layer can serve as barrier metal. Therefore, such thefirst layer can prevent metal contained in the second layer fromdispersing in the insulating layer 1303 and the underlying semiconductorlayer 1302.

Sidewalls (sidewall spacers) 1308 are provided at the both sides of thegate electrode 1304. The sidewalls can be formed by forming aninsulating layer over a substrate using silicon oxide by CVD, and bybeing subjected to an anisotropic etching by an RIE (reactive ionetching) method.

The thin film transistor including the semiconductor layer 1302, theinsulating layer 1303, the gate electrode 1304, and the like can employvarious kinds of structures such as a single drain structure, an LDD(lightly doped drain) structure, and a gate overlapping drain structure.A thin film transistor having an LDD structure in which lowconcentration impurity regions 1310 are formed in the semiconductorlayer overlapped with the sidewalls, is shown here. In addition, asingle gate structure, a multi-gate structure, in which thin filmtransistors, to which gate voltage having the same potential in term ofequivalence is applied, are connected in series, or a dual-gatestructure in which a semiconductor layer is interposed between gateelectrodes can be applied.

The insulating layer 248 is formed by using an inorganic insulatingmaterial such as silicon oxide and silicon oxynitride, or an organicinsulating material such as an acrylic resin and a polyimide resin. Whena coating method such as spin coating and roll coater is used, afterapplying an insulating film material dissolved in an organic solvent, aninsulating layer may be formed by heat treatment. For example, a filmcontaining siloxane bonds is formed first by the coating method, and issubjected to heat treatment at 200 to 400° C. so as to obtain aninsulating layer. When an insulating layer formed by a coating method oran insulating layer which is planarized by reflow is formed as theinsulating layer 248, disconnection of a wiring provided over theinsulating layer can be prevented. Further, such a method can beeffectively used in a case of forming a multilayer wiring.

The first conductive layers 243 formed over the insulating layer 248 canbe provided to be intersected with a wiring formed in the same layer asthe gate electrode 1304. A multilayer wiring structure is formed. Bylaminating a plurality of insulating layers having the same function asthe insulating layer 248 and forming a wiring thereover, a multilayerstructure can be formed. The first conductive layer 243 serving as awiring is preferably formed using a laminated structure of titanium (Ti)and aluminum (Al),a laminated structure of molybdenum (Mo) and aluminum(Al), a combination of a low resistance material such as aluminum (Al)and barrier metal using a high melting point metal material such astitanium (Ti) and molybdenum (Mo).

FIG. 25B shows one example of employing a bottom-gate type thin filmtransistor. An insulating layer 205 is formed over a substrate 230having an insulated surface, and a thin film transistor is providedthereover. The thin film transistor includes a gate electrode 1304, aninsulating layer 1303 serving as a gate insulating layer, asemiconductor layer 1302, a channel protection layer 1309, an insulatinglayer 1305 serving as a protection layer, and an insulating layer 248serving as an interlayer insulating layer. Further, an insulating layerserving as a protection layer may be provided thereover. The conductivelayer 243 can be formed over the insulating layer 1305 or the insulatinglayer 248. Note that the insulating layer 205 may not be provided in thecase of the bottom-gate type thin film transistor.

In a case where the substrate 230 having the insulated surface is aflexible substrate, the substrate 230 has lower heat resistance ascompared to a non-flexible substrate such as a glass substrate.Therefore, the thin film transistor is preferably formed using anorganic semiconductor.

Here, a structure of a thin film transistor formed using an organicsemiconductor will be described with reference to FIGS. 25C and 25D.FIG. 25C shows an example of applying a staggered organic semiconductortransistor. An organic semiconductor transistor is provided over aflexible substrate 1401. The organic semiconductor transistor includes agate electrode 1402, an insulating layer 1403 serving as a gateinsulating film, a semiconductor layer 1404 being overlapped with thegate electrode and the insulating layer 1403 serving as the gateinsulating film, and a conductive layer 243 serving as a wiringconnected to the semiconductor layer 1404. Further, the semiconductorlayer 1404 is in contact with the insulating layer 1403 serving as thegate insulating film and the conductive film 243 serving as the wiring.

The gate electrode 1402 can be formed using the same material and thesame method as the gate electrode 1304. Further, the gate electrode 1402can also be formed by a droplet discharging method and by drying andbaking. Furthermore, a paste containing a conductive fine particle isprinted over a flexible substrate by printing and the paste is dried andbaked so as to form the gate electrode 1402. As a typical example of theconductive fine particle, a fine particle mainly containing any one ofgold, copper, an alloy of gold and silver, an alloy of gold and copper,an alloy of silver and copper, and an alloy of gold, silver, and coppermay be used. In addition a fine particle mainly containing conductiveoxide such as indium tin oxide (ITO) may be used.

The insulating layer 1403 serving as the gate insulating film can beformed using the same material through the same method as the insulatinglayer 1303. Note that when an insulating layer is formed by heattreatment after applying an insulating film material dissolved in anorganic solvent, the heat treatment is performed at a lower temperaturethan an allowable temperature limit of the flexible substrate.

As a material for the semiconductor layer 1404 of the organicsemiconductor transistor, a polycyclic aromatic compound, a conjugateddouble bond compound, phthalocyanine, a charge transfer complex, and thelike can be given. For example, anthracene, tetracene, pentacene, 6T(hexathiophene), TCNQ (tetra-cyanoquinodimethane), PTCDA (a perylenecarboxylic acid anhydrous compound), NTCDA (a naphthalenecarboxylic acidanhydrous compound), and the like can be given. Further, as a materialfor the semiconductor layer 1404 of the organic semiconductortransistor, a n-conjugated system high molecule such as an organic highmolecular compound, carbon nanotube, polyvinyl pyridine, aphthalocyanine metal complex, and the like can be given. In particular,a π-conjugated system high molecule composed of a conjugated double bondsuch as polyacetylene, polyaniline, polypyrrole, polythienylene, apolythiophene derivative, poly(3alkylthiophene), a polyparaphenylenederivative, and a polyparaphenylenevinylene derivative, is preferablyused.

As a method for forming the semiconductor layer of the organicsemiconductor transistor, a method for forming a film having a uniformthickness may be used. The thickness of the semiconductor layer ispreferably set to be 1 nm or more and 1,000 nm or less, and morepreferably, 10 nm or more and 100 nm or less. As a specific method ofthe organic semiconductor transistor, an evaporation method, a coatingmethod, a spin coating method, a solution cast method, a dipping method,a screen printing method, a roll coater method, or a droplet dischargingmethod can be used.

FIG. 25D shows an example of applying a coplanar type organicsemiconductor transistor. An organic semiconductor transistor isprovided over a flexible substrate 1401. The organic semiconductortransistor includes a gate electrode 1402, an insulating layer 1403serving as a gate insulating film, conductive layers 243, and asemiconductor layer 1404 being overlapped with the gate electrode andthe insulating layer 1403 serving as the gate insulating layer. Further,each of the first conductive layers 243 serving as a wiring is incontact with the insulating layer serving as the gate insulating layerand the semiconductor layer.

Further, the thin film transistor and the organic semiconductortransistor may be provided to have any structure so long as they canserve as switching elements.

Furthermore, a transistor may be formed using a single crystallinesubstrate or an SOI substrate, and a memory element may be providedthereover. The SOI substrate may be formed by using a method in which awafer is attached, a method of forming an insulating layer in aninterior portion by doping a Si substrate with an oxygen ion, which isalso referred to as an SIMOX. Here, as shown in FIG. 17C, a memoryelement 241 is connected to a field-effect transistor 262 provided overa single crystalline semiconductor substrate 260. Further, an insulatinglayer 250 is provided to cover a wiring of the field-effect transistor262, and a memory element 241 is provided over the insulating layer 250.

Since the transistor formed using such a single crystallinesemiconductor has good characteristics such as high response speed andgood mobility, the transistor can be operated at high speed. Further,such a transistor has slight variations in its characteristics, andtherefore, a highly-reliable semiconductor device can be provided byusing the transistor.

The memory element 241 includes a first conductive layer 264 formed overthe insulating film 250, an organic compound layer 244 covering thefirst conductive layer 243 and the partition walls (insulating layers)249, and a second conductive layer 245. Note that the partition walls(insulating layers) 249 for covering one part of the first conductivelayer is formed.

Accordingly, by forming the memory element 241 after forming theinsulating layer 250, the first conductive layer 264 can be freelyarranged. That is, the memory element 241 must be provided in a regionoutside of a wiring of the transistor 240, in the structure as shown ineach of FIGS. 17A and 17B; however, by using the above structure, forexample, the memory element 241 can be formed over the transistor 262,which is provided in a layer 251 having transistors. As a result, memorydevice 216 can be highly integrated.

In each of FIGS. 17B and 17C, the organic compound layer 244 is providedover an entire surface of the substrate. Alternatively, organic compoundlayers 244 may be selectively provided only in respective memory cells.In this case, an organic compound is discharged by using a dropletdischarging method or the like and baked to selectively form organiccompound layers, making it possible to improve material use efficiency.

The first conductive layers 243 and 264 and the second conductive layer245 can be formed using the same material through the same method shownin Embodiment Mode 1.

Further, the organic compound layers 244 can be provided by using thesame material through the same method shown in Embodiment Mode 1.

Furthermore, an element having a rectifying property may be providedbetween the first conductive layers 243 and the organic compound layer244, and the first conductive layer 264 and the organic compound layer244, respectively. The element having a rectifying property is atransistor whose gate and drain electrodes are connected to each otheror a diode. Further, an element having the rectifying property may beprovided between the organic compound layer 244 and the secondconductive layer 245.

Moreover, after a separation layer is provided over the substrate 230having the insulated surface and a layer 253 having a transistor and amemory element 241 are provided over the separation layer, the layer 253having the transistor and the memory element 241 may be separated fromthe separation layer and may be attached to a substrate 461 through anadhesive layer 462 (see FIG. 20). As a separation method, the followingfour methods and the like can be employed: a separation method 1 where ametal oxide layer is provided as a separation layer between a substratehaving an insulated surface and a layer having a transistor, and themetal oxide layer is weakened by crystallization so as to separate thelayer having the transistor from the substrate by physical means; aseparation method 2 where an amorphous silicon film containing hydrogenis provided as a separation layer between a substrate having aninsulated surface and a layer having a transistor, and hydrogen gascontained in the amorphous silicon film is released by laser irradiationso as to separate the substrate having high heat resistance, or anamorphous silicon film is provided as a separation layer and theamorphous silicon film is removed by etching so as to separate the layerhaving the transistor; a separation method 3 where a substrate havinghigh heat resistance over which a layer having a transistor is provided,is mechanically removed or removed by etching with a use of a solutionor halogen fluoride gas such as NF₃, BrF₃, and ClF₃; and a separationmethod 4 where after a metal layer and a metal oxide layer are providedas separation layers between a substrate having an insulated surface anda layer having a transistor, the metal oxide layer is weakened bycrystallization, and a part of the meal layer is removed by etching witha use of a solution or halogen fluoride gas such as NF₃, BrF₃, and ClF₃,and then the weakened metal oxide layer is physically separated.

When a flexible substrate like the substrate 30 shown in Embodiment Mode1, a film having a thermoplastic property, a paper made from a fibrousmaterial, or the like is used as the substrate 461, a small, thin, andlightweight memory device can be realized.

Next, an operation in writing date in the memory device 216 will bedescribed (FIGS. 16A and 16B).

When writing data by applying voltage, one memory cell 221 is selectedby a row decoder 224 a, a column decoder 226 a, and a selector 226 c,and then data is written in the memory cell 221 using a write circuit(See FIG. 16A). A layer formed of a light emitting material emits lightby applying voltage between the first conductive layer 243 and thesecond conductive layer 245 in the memory cell. With the emissionenergy, the photosensitized oxidation reduction agent in the organiccompound layer come to an excited state. Furthermore, the substancebrings about chemical reactions by the excited photosensitized oxidationreduction agent, and chemical reactants are generated. As a result,electric resistance of the memory element is varied.

As compared to other memory elements before writing in, electricresistance of the memory element having the chemical reactants isvaried. By applying voltage to the memory cell, data is written in thememory cell while utilizing a change in electric resistance between twoconductive layers. For example, when data “1” is written in, in the casewhere the memory cell is in the state of data “0”, resistance is changedby selectively applying larger voltage to the organic compound layer ofa desired memory element.

Here, a case of writing data in a memory cell 221 in the m-th column andthe n-th row, will be described. In this case, a bit line Bm in the m-thcolumn and a word line Wn in the n-th row are selected by a row decoder224 a, a column decoder 226 a, and a selector 226 c, and a transistor240 included in the memory cell 221 in the m-th column and the n-th rowis turned on. Subsequently, voltage is applied between the firstconductive layer 243 and the second conductive layer 245 in the memorycell, and the layer formed of the light emitting material emits light.Note that the second conductive layer 245 of the memory element 241 isconnected to a common electrode with potential Vcom. With the emissionenergy, the photosensitized oxidation reduction agent in the organiccompound layer comes to the one in an excited state. Furthermore, thesubstance causes chemical reactions by the excited photosensitizedoxidation reduction agent, and chemical reactants are generated. As aresult, electric resistance of the memory element is changed.

Next, an operation in reading out data by applying voltage will bedescribed (see FIGS. 16A to 6C.). Data readout is performed by utilizinga difference in electric characteristics of the memory elements 241included in a memory cell having the data “0” and a memory cell havingthe data “1”. For example, a method for reading out data by utilizing adifference in electric resistance in a case where electric resistance ofthe memory elements included in the memory cell having the data “0” isR0 at a reading voltage and electric resistance of the memory cellhaving data “1” is R1 at a reading voltage, will be described. Note thatR1<R0. Here, a readout portion of the readout circuit 226 b has astructure including a resistance element 246 and a sense amplifier 247.The resistance element 246 has resistance value Rr, wherein R1<Rr<R0. Atransistor 254 may be used as a substitute for the resistance element246, or a clocked inverter 255 may be used as a substitute for the senseamplifier 247 (FIG. 16C). Needless to say, the structure of a circuit isnot limited thereto shown in FIG. 16C.

Data readout is performed by reading electric resistance of the organiccompound layer 244 by applying voltage between the first conductivelayer 243 and the second conductive layer 245. For example, a case ofreading data in a memory cell 221 in the m-th column and the n-th row,among plural memory cells 221 included in the memory cell array 222,will be described. In this case, a bit line Bm in the m-th column and aword line Wn in the n-th row are selected by a row decoder 224 a, acolumn decoder 226 a, and a selector 226 c. Specifically, apredetermined voltage of 24V, is applied to a word line Wy connected tothe memory cell 221 by the row decoder 224 a and the transistor 240 isturned on. A bit line Bx connected to the memory cell 221 is connectedto a terminal P of the readout circuit 226 b by the column decoder 226 aand the selector 226 c. As a result, potential Vp of the terminal Pbecomes a value which is determined by Vcom and V0, which are valuesdetermined by resistance division of the resistance element 246(resistance value Rr) and the memory element 241 (resistance value R0 orR1). Therefore, in a case where the memory cell 221 has the data “0”,Vp0=Vcom+(V0−Vcom)×R0/(R0+Rr). When the memory cell 221 has the data“1”, Vp1=Vcom+(V0−Vcom)×R1/(R1+Rr). As a result, by selecting Vref to bebetween Vp0 and Vp1 in FIG. 16B, Lo/Hi (or Hi/Lo) of an output potentialVout is output in accordance with the data “0” or data “1”, and hence,the data can be read out.

For example, the sense amplifier 47 is operated with Vdd=3 V, and Vy=0V; V0=3 V; and Vref=1.5 V. If R0/Rr=Rr/R1=9 and on-resistance of thetransistor 240 can be ignored, when the memory cell has the data “0”,Vp0 becomes 2.7 V and Hi is output as Vout. When the memory cell has thedata “1”, Vp1 becomes 0.3 V and Lo is output as Vout. Thus, data can beread out from the memory cell.

Subsequently, operation in reading out data of a memory element byapplying voltage in the case of using a transistor as a resistanceelement will be described by giving a specific example in FIG. 21.

FIG. 21 shows a current-voltage characteristic 951 of a memory elementin which the data “0” is written, a current-voltage characteristic 952of a memory element in which the data “1” is written, and acurrent-voltage characteristic 953 of a transistor. Further, a casewhere 3 V is applied between the first conductive layer 243 and thesecond conductive layer 245 as operation voltage when reading out data,will be described.

In FIG. 21, in a memory cell having the memory element, in which data“0” is written, an intersection point 954 of the current-voltagecharacteristic 951 of the memory element with the current-voltagecharacteristic 953 of the transistor is an operation point. In thiscase, potential of a node P becomes V2 (V). A potential of the node P issupplied to the sense amplifier 247. In the sense amplifier 247, datastored in the memory cell is determined as “0”.

On the other hand, in a memory cell having the memory element, in whichthe data “1” is written, an intersection point 955 of thecurrent-voltage characteristic 952 of the memory element with thecurrent-voltage characteristic 953 of the transistor is an operationpoint. In this case, potential of the node P becomes V1 (V) (V1<V2). Thepotential of the node P is supplied to the sense amplifier 247. In thedifferential amplifier 247, data stored in the memory cell is determinedas “1”.

By reading out potential which is subjected to resistance division inaccordance with a resistance value of the memory elements 241, datastored in the memory cell can be determined.

According to the above described method, data is read out by voltagevalue while utilizing a difference in resistance values of the memoryelements 241 and resistance division; however, information stored in thememory elements 241 may be read out by amount of current.

Furthermore, this embodiment mode can be implemented by being freelycombined with the above described embodiment modes.

Embodiment Mode 10

In this embodiment mode, an example of a semiconductor device typifiedby wireless chip having a memory device as shown in the above describedembodiment modes will be described with reference to the drawings.

One feature of the semiconductor device shown in this embodiment mode isthat data can be read out from and written in the semiconductor devicewithout contact. Data transmitting types can be largely classified intothree of an electromagnetic coupling type in which a pair of coils isplaced to face each other and communication is performed by mutualinduction; an electromagnetic induction type in which communication isperformed by an induction field; and a radio wave type in whichcommunication is performed by utilizing radio waves. Any type can beemployed. Further, there are two types of layouts of an antenna used fortransmitting data: one is a case where an antenna is provided over asubstrate over which a transistor and a memory element are provided; andthe other is a case where a terminal portion is provided over asubstrate over which a transistor and a memory element are provided andan antenna, which is provided over the other substrate, is connected tothe terminal portion.

First, a structural example of a semiconductor device in a case where anantenna is provided over a substrate over which a plurality of elementsand a plurality of memory elements are provided will be described withreference to FIGS. 18A and 18B.

FIG. 18A shows a semiconductor device having a passive matrix typememory circuit. Over a substrate 350, the semiconductor device includesa layer 351 having transistors 451 and 452, a memory element portion 352formed over the layer 351 having the transistors, and a conductive layer353 serving as an antenna.

Note that a case where the semiconductor device includes the memoryelement portion 352 and the conductive layer 353 serving as an antennaover the layer 351 having the transistors; however, the presentinvention is not limited thereto. The memory element portion 352 orconductive layer 353 serving as an antenna may be provided under or inthe same layer as the layer 351 having the transistors.

The memory element portion 352 has a plurality of memory elements 352 aand 352 b. The memory element 352 a includes a first conductive layer361 formed over an insulating layer 252, an organic compound layer 362 acovering the first conductive layer 361 and partition walls (insulatinglayers) 374, and a second conductive layer 363 a. Note that thepartition walls (insulating layers) 374 covers a part of the firstconductive layer. The memory element 352 b includes the first conductivelayer 361 formed over the insulating layer 252, the partition walls(insulating layers) 374 partly covering the first conductive layer, theorganic compound layer 362 b covering the first conductive layer 361 andthe partition walls (insulating layers) 374, and the second conductivelayer 363 b. Note that the partition walls (insulating layers) 374 covera part of the first conductive layer.

Further, an insulating layer 366 serving as a protection film is formedto cover the second conductive layers 363 a and 363 b and the conductivelayer 353 serving as an antenna. The first conductive layer 361 of thememory element portion 352 is connected to a wiring of a transistor 452.The memory element portion 352 can be formed using the same materialthrough the same manufacturing method as those shown in the aboveembodiment modes.

In the memory element portion 352, as shown in the above embodimentmodes, an element having a rectifying property may be provided betweenthe first conductive layer 361 and the organic compound layers 362 a and362 b, or between the organic compound layers 362 a and 362 b and thesecond conductive layers 363 a and 363 b. The same element having therectifying property described in Embodiment Mode 7 can be used as theelement having the rectifying property.

In this embodiment mode, the conductive layer 353 serving as an antennais provided over the conductive layer 360 which is formed in the samelayer as the second conductive layers 363 a and 363 b. Note that, theconductive layer serving as an antenna may be formed in the same layeras the second conductive layers 363 a and 363 b. The conductive layer353 serving as an antenna is connected to a source wiring or a drainwiring of the transistor 451.

As a material for the conductive layer 353 serving as the antenna, oneelement selected from gold (Au), platinum (Pt), nickel (Ni), tungsten(W), molybdenum (Mo), cobalt (Co), copper (Cu), aluminum (Al), manganese(Mn), titanium (Ti), and the like; or an alloy containing a plurality ofthe above mentioned elements; and the like can be given. As a method forforming the conductive layer 353 serving as the antenna, evaporation,sputtering, CVD, various kinds of printing methods such as screenprinting and gravure printing, a droplet discharging method, or the likecan be used.

The transistors 240 and 262 shown in Embodiment Mode 8 can be properlyused as the transistors 451 and 452 contained in the layer 351 havingthe transistors.

Furthermore, a separation layer, the layer 351 having the transistors,the memory element portion 352, and the conductive layer 353 serving asthe antenna are provided over a substrate, and the layer 351 having thetransistors, the memory element portion 352, and the conductive layer353 serving as the antenna are separated from the substrate by propertyusing the separation method mentioned in Embodiment Mode 8. Thereafter,the layer 351 having the transistors, the memory element portion 352,and the conductive layer 353 serving as the antenna separated from thesubstrate may be attached to another substrate by using an adhesivelayer. Utilizing a flexible substrate shown as the substrate 30 inEmbodiment Mode 1, a film having a thermoplastic property, a paper madefrom a fibrous material, a base material film, or the like as the othersubstrate makes it possible to achieve a small, thin, and lightweightmemory device.

FIG. 18B shows an example of a semiconductor device having an activematrix type memory circuit. Portions different from those of FIG. 18Awill be described in FIG. 18B.

The semiconductor device shown in FIG. 18B includes the layer 351 havingthe transistors 451 and 452 over the substrate 350, a memory elementportion 356 over the layer 351 having the transistors, and theconductive layer 353 serving as the antenna over the layer 351 havingthe transistors. Note that, a case where the transistor 452 serving as aswitching element of the memory element portion 356 is formed in thesame layer as the transistor 451 and the memory element portion 356 andthe conductive layer 353 serving as the antenna are formed over thelayer 351 having the transistors, is shown here; however, the memoryelement portion 356 and the conductive layer 353 serving as the antennacan be formed under or in the same layer as the layer 351 having thetransistors.

The memory element portion 356 includes the memory elements 356 a and356 b. The memory element 356 a includes first conductive layer 371 aformed over the insulating layer 252, an organic compound layer 372covering the first conductive layer 371 a and the partition walls(insulating layers) 374, and the second conductive layer 373. Note thatthe partition walls (insulating layers) 374 cover a part of the firstconductive layer 371 a. The memory element 356 b includes the firstconductive layer 371 b formed over the insulating layer 252, the organiccompound layer 372 covering the first conductive layer 371 and thepartition walls (insulating layers) 374. Note that the partition walls(insulating layers) 374 cover a part of the first conductive layer 371b. The first conductive layer 371 a and the first conductive layer 371 bare connected to wirings of each of the transistors. That is, the memoryelements are connected to each transistor.

Note that the same material and the same manufacturing method as shownin Embodiment Modes 1 and 7 can be used for forming the memory elements356 a and 356 b. Further, in the memory elements 356 a and 356 b, asdescribed above, an element having a rectifying property may be providedbetween the first conductive layers 371 a and 371 b and the organiccompound layer 372 or between the organic compound layer 372 and thesecond conductive layer 373.

The conductive layer formed with the layer 351 having the transistors,the conductive layer formed with the memory element portion 356, and theconductive layer 353 serving as the antenna can be formed by usingevaporation, sputtering, CVD, printing, a droplet discharging method, orthe like as described above. Further, they may be formed by differentmethods depending on their portions to be formed.

Furthermore, a separation layer, the layer 351 having the transistors,the memory element portion 356, and the conductive layer 353 serving asthe antenna may be provided over a substrate, the layer 351 having thetransistors, the memory element portion 356, and the conductive layer353 serving as the antenna may be separated from the substrate byproperty using the separation method shown in Embodiment Mode 8. Thelayer 351 having the transistors, the memory element portion 356, andthe conductive layer 353 serving as the antenna separated from thesubstrate may be attached to the other substrate having flexibility byusing an adhesive layer. By utilizing a flexible substrate shown as thesubstrate 30 in Embodiment Mode 1, a film having a thermoplasticproperty, a paper made from a fibrous material, a base material film, orthe like as the other substrate, it is possible to achieve a small,thin, and lightweight memory device.

Note that a sensor may be provided to be connected to the transistors.As a sensor, an element which detects temperature, humidity,illuminance, gas, gravity, pressure, sound (vibration), acceleration,and other characteristics by physical means or chemical means, can begiven. The sensor is typically formed using an element such as aresistance element, a capacitance coupled element, aninductively-coupled element, a photovoltaic element, a photoelectricconversion element, a thermo-electromotive element, a transistor, athermistor, and a diode.

Next, a structural example of a semiconductor device including a firstsubstrate, which includes a layer having transistors, a terminal portionbeing connected to the transistors, and a memory element, and a secondsubstrate over which an antenna being connected to the terminal portion,will be described with reference to FIGS. 19A and 19B. Note that,portions different from those of FIGS. 18A and 18B will be described inFIGS. 19A and 19B.

FIG. 19A shows a semiconductor device having a passive matrix typememory circuit. The semiconductor device includes a layer 351 havingtransistors formed over a substrate 350, a memory element portion 352formed over the layer 351 having the transistors, a connection terminal368 being connected to the transistor 451, and a substrate 365 overwhich a conductive layer 357 serving as an antenna is provided. Theconductive layer 357 is connected to the connection terminal 368 byconductive particles 359. Note that, a case in which the memory elementportion 352 is provided over the layer 351 having the transistors, isshown here; however, the present invention is not limited thereto.Alternatively, the memory element portion 352 may be provided under orin the same layer as the layer 351 having the transistors.

The memory element portion 352 can be formed using the memory elementportion 352 having the structure as shown in FIG. 18A.

Further, the substrate including the layer 351 having the transistorsand the memory element portion 352 and the substrate 365 including theconductive layer 357 serving as the antenna are attached to each otherwith a resin 375 having an adhesion property. The layer 351 having thetransistors and a conductive layer 357 are electrically connected toeach other through the conductive particles 359 contained in the resin375. Alternatively, the substrate 350 including the layer 351 having thetransistors and the memory element portion 352 and the substrate 365including the conductive layer serving as the antenna, may be attachedto each other by using a conductive adhesive agent such as a silverpaste, a copper paste, and a carbon paste or a solder joint method.

FIG. 19B shows a semiconductor device having the memory device shown inEmbodiment Mode 9. The semiconductor device includes a layer 351 havingtransistors 451 and 452 formed over a substrate 350, a memory elementportion 356 formed over the layer 351 having the transistors, aconnection terminal 368 being connected to the transistor 451, and asubstrate 365 over which a conductive layer 357 serving as an antenna isprovided. The conductive layer 357 and the connection terminal 378 areconnected to each other by conductive particles 359. Note that a casewhere in the layer 351 having the transistors 451 and 452, thetransistor 451 is formed in the same layer as the transistor 452 and theconductive layer 357 serving as the antenna is formed over the layer 351having the transistors, is shown here; however, the present invention isnot limited thereto. Alternatively, the memory element portion 356 maybe provided under or in the same layer as the layer 351 having thetransistors.

The memory element portion 356 can be formed using the memory elements356 a and 356 b having the structure shown in FIG. 18B.

Also, in FIG. 19B, the substrate 350, which includes the layer 351having the transistors and the memory element portion 356, and thesubstrate 365, over which the conductive layer 357 serving as theantenna is provided, are attached to each other by a resin 375containing the conductive particles 359. Further, the conductive layer357 and the connection terminal 378 are connected to each other by theconductive particles 359.

Furthermore, a separation layer, the layer 351 having the transistors,and the memory element portion 356 may be provided over a substrate, andthe layer 351 having the transistors and the memory element portion 356may be separated from the substrate by using the separation method shownin Embodiment Mode 9. The layer 351 having the transistors and thememory element portion 356 may be attached to the substrate 461 by usingan adhesive layer having flexibility.

Moreover, each of the memory element portions 352 and 356 may beprovided over the substrate 365 over which the conductive layer servingas the antenna is provided. Specifically, a first substrate over which alayer having transistors is provided, and a second substrate over whicha memory element portion and a conductive layer serving as an antennaare provided, may be attached to each other by using a resin containingconductive particles. A sensor being connected to the transistors mayalso be provided as well as the semiconductor devices shown in FIGS. 18Aand 18B.

Furthermore, the present embodiment mode can be implemented by beingfreely combined with the above described embodiment modes.

Embodiment Mode 11

In this embodiment mode, a light emitting material which can be used ina memory element shown in Embodiment Mode 1 to Embodiment Mode 6, amemory device shown in Embodiment Mode 8 and Embodiment Mode 9, and asemiconductor device shown in Embodiment Mode 10 are described asfollows.

A light emitting element formed using an inorganic compound as a lightemitting material can be used in a light emitting element portion shownin Embodiment Mode 5 and Embodiment Mode 6. Typically, an inorganic ELelement utilizing electroluminescence can be given.

The inorganic EL element is classified into a dispersed inorganic ELelement or a thin film inorganic EL element depending on the elementconstitution. They are different in that the former has anelectroluminescence layer in which particles of the light emittingmaterial are dispersed in a binder, and the latter has anelectroluminescence layer formed of a thin film made of a light emittingmaterial; however, a common point is that they both require electronswhich are accelerated at high electric field. As a mechanism of theobtained emission, there are two types: donor-acceptor recombinationemission in which a donor level and an acceptor level are used, andlocal emission in which inner shell electron transition in a metal ionis used. Generally, the dispersed inorganic EL element typically has adonor-acceptor recombination emission and the thin film inorganic ELelement typically has local emission.

The light emitting material which can be used in this embodiment mode isformed of a host material and an impurity element which becomes thecenter of the emission. By changing the included impurity element to beincluded, variety of colors of emission can be obtained. As amanufacturing method of the light emitting material, various methodssuch as a solid phase method, a liquid phase synthesis method(coprecipitation method), or the like can be used. Alternatively, aspraying thermal decomposition method, a double decomposition method, amethod by thermal decomposition reaction of a precursor, a reversedmicelle method, a method in which these methods and high temperaturefiring are combined, a solution synthetic method such as a freeze-dryingmethod, or the like can be used.

The solid phase method is a method in which a compound including a hostmaterial and an impurity element or a compound including the impurityelement are weighed, mixed in a mortar, heated in an electric-furnaceand baked to react so as to include an impurity element in the hostmaterial. The baking temperature is preferably 700° C. to 1500° C. Thisis because solid-phase reaction does not proceed when temperature is toolow, and the host material is decomposed when temperature is too high.The baking may be performed in a powder state; however, it is preferablyperformed in a pellet state. Baking at a comparatively high temperatureis required. However, since it is a simple method, high productivity canbe obtained; therefore, it is suitable for mass-production.

The liquid phase synthesis method (coprecipitation method) is a methodin which a host material or a compound including the host material, andan impurity element or a compound including the impurity element arereacted in a solution, dried, and then baked. The particles of the lightemitting material are dispersed uniformly, and the reaction is advancedeven if the particles are small and baking temperature is low.

As the host material to be used for the light-emitting material, asulfide, an oxide, or a nitride can be used. As a sulfide, zinc sulfide(ZnS), cadmium sulfide (CdS), calcium sulfide (CaS), yttrium sulfide(Y₂S₃), gallium sulfide (Ga₂S₃), strontium sulfide (SrS), barium sulfide(BaS), or the like can be used. As an oxide, for example, zinc oxide(ZnO), yttrium oxide (Y₂O₃), or the like can be used. As an nitride,aluminum nitride (AlN), gallium nitride (GaN), indium nitride (InN), orthe like can be used. Alternatively, zinc selenide (ZnSe), zinctelluride (ZnTe), or the like can be also used. Furthermore, mixedcrystal of a three-dimensional structure such as calcium sulfide-gallium(CaGa₂S₄), strontium sulfide-gallium (SrGa₂S₄), and bariumsulfide-gallium (BaGa₂S₄) may be used.

As a luminescence center of the local emission, manganese (Mn), copper(Cu), samarium (Sm), terbium (Tb), erbium (Er), thulium (Tm), europium(Eu), cerium (Ce), praseodymium (Pr), or the like can be used. As chargecompensation, a halogen element such as fluorine (F), chlorine (Cl) maybe added.

On the other hand, as a luminescence center of the donor-acceptorrecombination emission, a light emitting material including a firstimpurity element forming a donor level and a light emitting materialincluding a second impurity element forming an acceptor level can beused. As the first impurity element, for example, fluorine (F), chlorine(Cl), bromine (Br), Iodine (I), boron (B), aluminum (Al), gallium (Ga),indium (In), thallium (Tl), or the like can be used. As the secondimpurity element, for example, a metal element such as copper (Cu),silver (Ag), iron (Au), platinum (Pt), or silicon (Si) can be used.

When a light emitting material of donor-acceptor recombination emissionis synthesized by a solid phase method, a host material, a firstimpurity element or a compound including the first impurity element, anda second impurity element or a compound including the second impurityelement are weighed, mixed in a mortar, heated in an electric-furnaceand baked. As the host material, the above mentioned host materials canbe used. As the first impurity element or the compound including theimpurity element, for example, fluorine (F), chlorine (Cl), aluminumsulfide (Al₂S₃), or the like can be used. As the second impurity elementor the compound including the second impurity element, for example,copper (Cu), silver (Ag), copper sulfide (Cu₂S), silver sulfide (Ag₂S),or the like can be used. The burning temperature is preferably 700° C.to 1500° C. It is because a solid-phase reaction does not proceed whentemperature is too low, and the host material is decomposed whentemperature is too high. The baking may be performed in a powder state,however preferably performed in a pellet state.

As an impurity element in the case of using a solid-phase reaction, acombination of compounds formed of the first impurity element and thesecond impurity element may be used. In this case, since the impurityelement is easily dispersed and the solid-phase reaction is easilyadvanced, a uniform light emitting material can be obtained.Furthermore, since impurity element is not entered excessively, thelight emitting material with high purity can be obtained. As thecompound formed of the first impurity element and the second impurityelement, for example, copper fluoride (CuF₂), copper chloride (CuCl),copper iodide (CuI), copper bromide (CuBr), copper nitride (Cu₃N),copper phosphide (Cu₃P), silver fluoride (AgF), silver chloride (AgCl),silver iodide (AgI), silver bromide (AgBr), Auric chloride (AuCl₃),Auric bromide (AuBr₃), chlorination platinum (PtCl₂), or the like can beused.

Note that the concentration of these impurity elements is in the rangeof 0.01 to 10 atom % with respect to the host material, preferably, 0.05to 5 atom %.

As a light emitting material having a luminescence center of thedonor-acceptor recombination emission, a light emitting materialincluding the third impurity element may be used. As the third impurityelement, for example, lithium (Li), sodium (Na), potassium (K), rubidium(Rb), caesium (Cs), nitrogen (N), phosphorus (P), arsenic (As), antimony(Sb), bismuth (Bi), or the like can be used. In this case, theconcentration of the third impurity element is preferably 0.05 to 5%atom % with respect to the host material. Light emission at low voltageis possible by using the light emitting material having such astructure. Accordingly, a light emitting element which can emit light atlow driving voltage can be obtained, and a light emitting element withreduced power consumption can be obtained. Furthermore, the impurityelement which becomes the luminescence center of the local emission maybe included.

As the light emitting material, for example, a light emitting materialincluding ZnS as the host material, Cl as the first impurity element, Cuas the second impurity element, Ga and As as the third impurity element,and Mn as the luminescence center of the local emission may be used. Thefollowing method can be used to form such a light emitting material.First, Mn is added to the light emitting material (ZnS: Cu, Cl), andbaked for 2 to 4 hours in vacuum. The burning temperature is preferably700 to 1500° C. This baked material is powdered to have a grain size of5 to 20 μm, and GaAs having a grain size of 1 to 3 μm is added thereto,and is agitated. By baking this mixture in a nitrogen current of airincluding a sulfur gas at about 500 to 800° C. for 2 to 4 hours, thelight emitting material can be obtained. By using the light emittingmaterial to form a thin film by a vapor deposition method, the thin filmcan be used as a light emitting layer of the light emitting element.

Light emission is possible without using hot electrons which areaccelerated by high electric field in the light emitting layer using theabove mentioned material as a host material, and using the lightemitting layer made of the light emitting material including the firstimpurity element, the second impurity element and the third impurityelement. Namely, since it is not necessary to apply high voltage to thelight emitting element, the light emitting element which can operate atlow driving voltage can be obtained. Furthermore, since light emissionis possible at low driving voltage, a light emitting element in whichpower consumption is reduced can be obtained. Moreover, an element whichcan be another luminescence center can be included.

The inorganic EL element includes the above mentioned material as a hostmaterial, the second impurity element, the third impurity element andthe light emitting material having a luminescence center utilizing theinner shell electron transition in the metal ion. In this case, themetal ion which becomes the luminescence center is preferably 0.05 to 5atomic % with respect to the host material. The concentration of thesecond impurity element is preferably 0.05 to 5 atomic % with respect tothe host material. The concentration of the third impurity element ispreferably 0.05 to 5 atomic % to the host material. In the lightemitting material having such a structure, light emission at low voltageis possible. Since the light emitting element which can emits light atlow voltage can be obtained, a light emitting element with reduced powerconsumption can be obtained. Furthermore, an element which can beanother luminescence center may be included.

In the case of a thin film type inorganic EL, an electroluminescentlayer is a layer including the light emitting material, and can beformed by a vacuum evaporation method such as a resistance heating vaporevaporation method or electron-beam evaporation (EB deposition) method,a physical vapor deposition (PVD) method such as a sputtering method, anorganic metal CVD method, a chemical vapor deposition method such ashydride transfer low pressure CVD method (CVD), an atomic layer epitaxy(ALE) method, or the like.

An example of a thin film type inorganic EL element which can be used asa light emitting element is shown in FIGS. 26A to 26C. In FIGS. 26A to26C, the light emitting element includes a first conductive layer 50, anelectroluminescent layer 51, and a conductive layer 53 having alight-transmitting property.

The light emitting element shown in FIGS. 26B and 26C has a structure inwhich one or more insulating layer is provided between one or a pair ofconductive layers and an electroluminescent layer in a light emittingelement in FIG. 26A. The light emitting shown in FIG. 26B has aninsulating layer 54 between a first conductive layer 50 and anelectroluminescent layer 52, and the light emitting element shown inFIG. 26C has an insulating layer 54 a between the first conductive layer50 and the electroluminescent layer 52, and an insulating layer 54 bbetween the conductive layer 53 having a light-transmitting property andthe electroluminescent layer 52. The insulating layer may be providedbetween the electroluminescent layer and a conductive layer or theinsulating layers may be provided between the electroluminescent layerand the pair of the electrode layers. Furthermore, the insulating layermay be a single layer or a lamination layer formed of a plurality oflayers.

The insulating layer 54 is provided so as to have contact with the firstconductive layer 50 in FIG. 26B, however the insulating layer 54 may beprovided so as to have contact with the conductive layer 53 having alight-transmitting property by reversing the order of the insulatinglayer and the electroluminescent layer.

In the case of the dispersed inorganic EL, particulate light emittingmaterials are dispersed in a binder, thereby forming a membranouselectroluminescent layer. When a particle having a size that isdesirably enough can not be obtained, it can be processed by crushing inmortar or the like to have adequate particulate light emittingmaterials. The binder is a substance for fixing the granular lightemitting material in a dispersed state, and holding in a form of anelectroluminescent layer. The light emitting material is uniformlydispersed in the electroluminescent layer by the binder and fixed.

In the case of the dispersed inorganic EL, the electroluminescent layercan be formed by a droplet discharge method in which anelectroluminescent layer can be selectively formed, a printing method(screen printing, offset printing, or the like), a coating method suchas spin coating, dipping method, a dispenser method, or the like. Thefilm thickness is not specifically limited; however, it is preferablyfrom 10 nm to 1000 nm. In the electroluminescent layer including a lightemitting material and a binder, the ratio of the light emitting materialis preferably from 50 wt % to 80 wt %.

An example of the dispersed inorganic EL element which can be used as alight emitting element is shown in FIG. 27A to FIG. 27C. The lightemitting element in FIG. 27A has a laminated structure of the firstconductive layer 60, the electroluminescent layer 62, and the conductivelayer 63 having a light-transmitting property. And the light emittingelement 61 kept by the binder is included in the electroluminescentlayer 62.

As the binder which can be used in this embodiment mode, an insulatingmaterial can be used. In addition, an organic material or an inorganicmaterial, or a mixed material of the organic material and the inorganicmaterial can be used. As the organic insulating material, like acyanoethyl cellulose resin, a polymer having a relatively highdielectric constant, resin such as polyethylene, polypropylene,polystyrenic resin, silicon resin, epoxy resin, vinylidene fluoride, orthe like can be used. Alternatively, a thermally stable polymer such asaromatic polyamide and polybenzimidazole, or a siloxane resin may beused. Note that the siloxane resin corresponds to a resin containing aSi—O—Si bond. In siloxane, a skeleton structure is constituted by a bondbetween silicon (Si) and oxygen (O). As a substituent, an organic groupat least including hydrogen (for example, alkyl group, aromatichydrocarbon) is used. As the substituent, a fluoro group may be used.Alternatively, an organic group at least including hydrogen and fluorogroup may be used as a substituent. Alternatively, a resin material suchas a vinyl resin like polyvinyl alcohol, polyvinyl butyral, or the like,a phenol resin, a novolac resin, an acrylic resin, a melamine resin, anurethane resin, or an oxazole resin (polybenz oxazole) can be used.Furthermore, a photo-curing resin material may be used. The dielectricconstant can be adjusted by adequately mixing fine particles of highdielectric constant such as barium titanate (BaTiO₃) or strontiumtitanate (SrTiO₃).

The inorganic insulating material included in the binder can be formedof silicon oxide (SiOx), silicone nitride (SiNx), silicon includingoxygen and nitrogen, aluminum nitride (AlN), aluminum including oxygenand nitrogen or aluminum oxide (Al₂O₃), titanium oxide (TiO₂), BaTiO₃,SrTiO₃, lead titanate (PbTiO₃), potassium niobate (KNbO₃), lead niobate(PbNbO₃), tantalum oxide (Ta₂O₅), barium tantalate (BaTa₂O₆), lithiumtantalate (LiTaO₃), yttrium oxide (Y₂O₃), zirconium oxide (ZrO₂), ZnS,or other material selected from a substance including other inorganicinsulating materials. By adding the inorganic material having a highdielectric constant in the organic material (using a doping method orthe like), the dielectric constant of the electroluminescent layer madefrom the light emitting material and the binder can be controlledfurther, and the dielectric constant can be increased further.

In a manufacturing step, a light emitting material is dispersed in asolution including a binder. As a solvent of solution including thebinder which can be used for this embodiment mode, a solvent in which abinder material is dissolved, and a solution having a viscosity suitablefor a method for manufacturing an electroluminescent layer (various wetprocesses) and for a desired film thickness can be formed, is properlyselected. In the case where the organic solvent or the like can be used,for example, a siloxane resin is used as a binder, propylene glycolmonomethylether, propylene glycol monomethylether acetate (also referredto as PGMEA), 3-methoxy-3 methyl-1-butanol (also referred to as MMB), orthe like can be used.

The light emitting element shown in FIGS. 27B and 27C has a structure inwhich one or more insulating layer is provided between one or a pair ofconductive layers and an electroluminescent layer in a light emittingelement in FIG. 27A. The light emitting shown in FIG. 27B has aninsulating layer 64 between a first conductive layer 60 and anelectroluminescent layer 62, and the light emitting element shown inFIG. 27C has an insulating layer 64 a between the first conductive layer60 and the electroluminescent layer 62, and an insulating layer 64 bbetween the conductive layer 63 having a light-transmitting property andthe electroluminescent layer 62. The insulating layer may be providedbetween the electroluminescent layer and a conductive layer or theinsulating layers may be provided between the electroluminescent layerand the pair of the electrode layers. Furthermore, the insulating layermay be a single layer or a lamination layer formed of a plural layers.

The insulating layer 64 is provided so as to have contact with the firstconductive layer 60 in FIG. 27B, however the insulating layer 64 may beprovided so as to have contact with the conductive layer 63 having alight-transmitting property by reversing the order of the insulatinglayer and the electroluminescent layer.

A first conductive layer 50 and a conductive layer 53 having alight-transmitting property in FIGS. 26A to 26C, a first conductivelayer 60 and a conductive layer 63 having a light-transmitting propertyin FIGS. 27A to 27C, a first conductive layer 101 shown in EmbodimentMode 5 and Embodiment Mode 6, and a conductive layer 141 having alight-transmitting property can be property used.

An insulating layer such as the insulating layer 54 in FIG. 26 and theinsulating layer 64 in FIG. 27 is not specifically limited; however itpreferably has a high insulation resistance, a fine film quality, and ahigh dielectric constant. For example, silicon oxide (SiO₂), yttriumoxide (Y₂O₃), titanium oxide (TiO₂), aluminum oxide (Al₂O₃), hafniumoxide (HfO₂), tantalum oxide (Ta₂O₅), barium titanate (BaTiO₃),strontium titanate (SrTiO₃), lead titanate (PbTiO₃), silicon nitride(Si₃N₄), or zirconium oxide (ZrO₂), a mixed layer of these, or alamination film including two or more kinds of these can be used. Theseinsulating films can be formed by sputtering, evaporation, CVD, or thelike. The insulating layer may be also formed by dispersing particles ofthese insulating materials in a binder. The material for the binder isformed of the same material as the binder included in theelectroluminescent layer using the same method. The film thickness isnot specifically limited; however, it is preferably in the range of 10nm to 1000 nm.

As the light emitting material shown in Embodiment Mode 1 to 4, the hostmaterial and the impurity element which becomes a luminescence centercan be properly used.

The light emitting element shown in this embodiment mode can obtainlight emission by applying voltage between a pair of electrode layerssandwiching the electroluminescent layer, however, the light emittingelement can operate either in AC drive or DC drive.

Embodiment 1

Here, a structure of a semiconductor device of this embodiment isdescribed with reference to FIGS. 22A to 22C. As shown in FIG. 22A, asemiconductor device 20 of this embodiment has a function to send andreceive data wirelessly, and also has a power source circuit 11, a clockgeneration circuit 12, a data modulation/demodulation circuit 13, acontrol circuit 14 which controls another circuit, an interface circuit15, a memory device 16, a bus 17, and an antenna 18.

Further, as shown in FIG. 22B, a semiconductor device 20 of thisembodiment has a function to send and receive data wirelessly, and alsohas a power source circuit 11, a clock generation circuit 12, a datamodulation/demodulation circuit 13, a control circuit 14 which controlsanother circuit, an interface circuit 15, a memory device 16, a bus 17,and an antenna 18. In addition, a central processing unit 71 may beincluded.

Further, as shown in FIG. 22C, a semiconductor device 20 of thisembodiment has a function to send and receive data wirelessly, and alsohas a power source circuit 11, a clock generation circuit 12, a datamodulation/demodulation circuit 13, a control circuit 14 which controlsanother circuit, an interface circuit 15, a memory device 16, a bus 17,an antenna 18, and a central processing unit 71. In addition, adetecting portion 72 including a detecting element 73 and a detectingcontrol circuit 74 may be included.

In a semiconductor device of this embodiment mode, a small andmultifunctional semiconductor device can be manufactured by forming adetecting portion 72 including a detecting element 73 and a detectingcontrol circuit, and the like in addition to a power source circuit 11,a clock generation circuit 12, a data modulation/demodulation circuit13, a control circuit 14 which controls another circuit, an interfacecircuit 15, a memory device 16, a bus 17, an antenna 18, and a centralprocessing unit 71

The power source circuit 11 is a circuit generating various powersources to be supplied to the respective circuits in the semiconductordevice 20 based on an alternating signal inputted from the antenna 18.The clock generation circuit 12 is a circuit generating various clocksignals to be supplied to the respective circuits in the semiconductordevice 20 based on an alternating signal inputted from the antenna 18.The data modulation/demodulation circuit 13 has a function tomodulate/demodulate data to be sent to or received from a reader/writer19. The control circuit 14 has a function to control the storage circuit16. The antenna 18 has a function to send and receive an electric fieldor an electric wave. The reader/writer 19 has a function to exchangedata with the semiconductor device, control semiconductor device, andcontrol the process of the data sent to or received from thesemiconductor device. The semiconductor device is not limited to theabove structure, and for example, another element such as a limitercircuit of power source voltage or hardware only for processing codesmay be added.

The memory device 16 has one or a more selected from the memory devicesshown in Embodiment Mode 8 or Embodiment Mode 9. Since the sizereduction, the decrease in film thickness, as well as the increase incapacitance can be achieved simultaneously in the memory elementincluding an organic compound, the semiconductor device can be compactand lightweight by forming the memory device 16 with the memory elementincluding the organic compound.

The detecting portion 72 can detect temperature, pressure, flow rate,light, magnetism, acoustic wave, acceleration, humidity, gasconstituent, liquid constituent, and other characteristics by a physicalor chemical means. Moreover, the detecting portion 72 has the detectingelement 73 for detecting a physical amount or a chemical amount and thedetecting control circuit 74 for converting the physical amount or thechemical amount detected by the detecting element 73 into an appropriatesignal such as an electric signal. As the detecting element 73, it ispossible to use a resistance element, a capacitance-coupled element, aninductively-coupled element, a photoelectromotive element, aphotoelectric conversion element, a thermoelectromotive element, atransistor, a thermistor, a diode, or the like. The number of detectionportions 30 may be more than one and, in such a case, it is possible todetect a plurality of physical amounts or chemical amountssimultaneously.

The physical amount described here means temperature, pressure, flowrate, light, magnetism, acoustic wave, acceleration, humidity, and thelike, while the chemical amount means a chemical substance such as a gasconstituent or a liquid constituent like ions, or the like. In addition,an organic compound such as a particular biological substance includedin blood, sweat, urine, or the like (for example, blood-sugar level inthe blood) is also included. In particular, in the case of detecting thechemical amount, since a particular substance needs to be selectivelydetected, a substance which selectively reacts with the substance to bedetected is provided in advance in the detecting element 73. Forexample, in the case of detecting a biological substance, it ispreferable to fix, in a polymer or the like, enzyme, a resistormolecule, a microbial cell, or the like which selectively reacts withthe biological substance to be detected by the detecting element 73.

Embodiment 2

According to this embodiment, a semiconductor device 20 serving as awireless chip can be formed. The semiconductor device serving as awireless chip can be applied over a wide range and specific examples ofthese applications are described hereinafter. The semiconductor device20 of the present invention can be applied to, for example, a banknote,a coin, documents of value, unregistered bonds, identificationcertificates (driver's license, certificate of residence, and the like,refer to FIG. 24A), pack cases (a pack paper, a bottle, and the like,refer to FIG. 24C), recording media (DVD software, a video tape, and thelike, refer to FIG. 24B), vehicles (a bicycle and the like, refer toFIG. 24D), personal belongings (a bag, glasses, and the like, foods,plants, animals, a human body, clothes, general merchandise, objectssuch as merchandises of electronic appliances, labels of goods (refer toFIGS. 24E and 24F) and the like. The electronic appliances include aliquid crystal display device, an EL display device, a television device(also referred to as simply a TV, a TV receiving machine, or atelevision receiving machine), a mobile phone, and the like.

The semiconductor device 20 of this embodiment is fixed to an object bymounting the device onto a print substrate, pasting the device to thesurface, or embedding the device inside the object. For example, if theobject is a book, the device is fixed to the book by embedding thedevice inside the paper, and if the object is a package made of anorganic resin, the device is fixed to the package by embedding thedevice inside the organic resin. Since the semiconductor device 20 ofthis embodiment is small, thin, and light-weight, the design quality isnot degraded even after the device is fixed to an object. By providingthe semiconductor device 20 of this embodiment to a banknote, a coin,documents of value, unregistered bonds, identification certificates, andthe like, an identification function can be provided, thereby preventingthe forgery. Moreover, by providing the semiconductor device 20 of thisembodiment for pack cases, recording media, personal belongings, foods,clothes, general merchandise, electronic appliances, and the like, asystem such as an inspection system becomes more efficient.

Next, a mode of the electronic appliance where the semiconductor deviceof this embodiment is mounted is described with reference to thedrawing. The electronic appliance shown here is a mobile phone includingcases 2700 and 2706, a panel 2701, a housing 2702, a printed circuitboard 2703, operation buttons 2704, a battery 2705, and the like (referto FIG. 23). The panel 2701 is detachably incorporated in the housing2702. The housing 2702 is fitted into the printed circuit board 2703.The shape and dimension of the housing 2702 are appropriately changed inaccordance with the electronic appliance where the panel 2701 is to beincorporated. Over the printed circuit board 2703, a plurality ofpackaged semiconductor devices are mounted and the semiconductor device20 of this embodiment can be used as one of the plurality of packagedsemiconductor devices. The plurality of semiconductor devices mountedonto the printed circuit board 2703 has any one of functions of acontroller, a central processing unit (CPU), a memory, a power sourcecircuit, an audio processing circuit, a sending/receiving circuit, andthe like.

The panel 2701 is connected to the printed circuit board 2703 through aconnection film 2708. The above panel 2701, the housing 2702, and theprinted circuit board 2703 are placed in the cases 2700 and 2706together with the operation buttons 2704 and the battery 2705. A pixelregion 2709 in the panel 2701 is provided so as to be observed throughan opening window provided in the case 2700.

As above, the semiconductor device of this embodiment is small, thin,and lightweight, whereby the limited space in the cases 2700 and 2706 ofthe electric appliance can be effectively used.

The semiconductor device of this embodiment includes a memory devicehaving a simple structure where an organic compound layer which ischanged by applied voltage from outside is sandwiched between a pair ofelectrodes, and therefore, electronic devices using an inexpensivesemiconductor device can be provided. Furthermore, since highintegration is easy in the semiconductor device of this embodiment,electronic devices using the semiconductor device having a high-capacitymemory device can be provided.

The memory device included in a semiconductor device of this embodimentis nonvolatile and additionally recordable in which data is written byapplied voltage from outside. With this characteristic, forgery byrewriting can be prevented and new data can be written additionally.Therefore, electronic devices using a sophisticated and high-value-addedsemiconductor device can be provided.

The cases 2700 and 2706 are shown as an example of an exterior shape ofthe mobile phone. The electronic appliance of this embodiment can bechanged variously in accordance with the function or the intendedpurpose thereof.

The present application is based on Japanese Priority Application No.2005-234387 filed on Aug. 12, 2005 with the Japanese Patent Office, theentire contents of which are hereby incorporated by reference.

1. A memory device having a memory element comprising: a firstconductive layer; a second conductive layer; and an organic compoundlayer between the first conductive layer and the second conductivelayer, wherein the organic compound layer comprises: a photosensitizedoxidation agent; and a substance, and wherein the photosensitizedoxidation agent is capable of oxidizing the substance at least partly.2. The memory device according to claim 1, wherein a voltage is appliedto the first conductive layer and the second conductive layer, whereinthe photosensitized oxidation agent is excited by recombination energyof holes and electrons generated by the voltage, and wherein the excitedphotosensitized oxidation agent is capable of oxidizing the substance atleast partly.
 3. The memory device according to claim 1, wherein aconductivity of the oxidized substance is different from a conductivityof the substance before oxidation.
 4. The memory device according toclaim 1, further comprising: a diode electrically connected to any oneof the first conductive layer and the second conductive layer.
 5. Thememory device according to claim 1, further comprising: a write circuitelectrically connected to a plurality of memory cells, wherein theplurality of the memory cells is arranged in a matrix form, and whereineach of the plurality of memory cells comprises the memory element. 6.The memory device according to claim 5, wherein each of the plurality ofmemory cells further comprises a transistor.
 7. A semiconductor devicecomprising: the memory device according to claim 1; a conductive layerserving as an antenna; and a transistor electrically connected to theconductive layer.
 8. The semiconductor device according to claim 7,further comprising any one of a readout circuit, a power source circuit,a clock generation circuit, a data modulation circuit, a datademodulation circuit, a control circuit and an interface circuit.
 9. Amemory device having a memory element comprising: a first conductivelayer; a second conductive layer; and an organic compound layer betweenthe first conductive layer and the second conductive layer, wherein theorganic compound layer comprises: a light emitting material; aphotosensitized oxidation agent; and a substance, and wherein thephotosensitized oxidation agent is capable of oxidizing the substance atleast partly.
 10. The memory device according to claim 9, wherein theorganic compound layer comprises: a first layer comprising the lightemitting material; and a second layer comprising the photosensitizedoxidation agent and the substance.
 11. The memory device according toclaim 9, wherein a voltage is applied to the first conductive layer andthe second conductive layer, wherein the light emitting material emitslight by recombination energy of holes and electrons generated by thevoltage, wherein the photosensitized oxidation agent is excited by thelight, and wherein the excited photosensitized oxidation agent iscapable of oxidizing the substance at least partly.
 12. The memorydevice according to claim 9, wherein a conductivity of the oxidizedsubstance is different from a conductivity of the substance beforeoxidation.
 13. The memory device according to claim 9, furthercomprising: a diode electrically connected to any one of the firstconductive layer and the second conductive layer.
 14. The memory deviceaccording to claim 9, further comprising: a write circuit electricallyconnected to a plurality of memory cells, wherein the plurality of thememory cells is arranged in a matrix form, and wherein each of theplurality of memory cells comprises the memory element.
 15. The memorydevice according to claim 14, wherein each of the plurality of memorycells further comprises a transistor.
 16. A semiconductor devicecomprising: the memory device according to claim 9; a conductive layerserving as an antenna; and a transistor electrically connected to theconductive layer.
 17. The semiconductor device according to claim 16,further comprising any one of a readout circuit, a power source circuit,a clock generation circuit, a data modulation circuit, a datademodulation circuit, a control circuit and an interface circuit.
 18. Amemory device having a memory element comprising; a first conductivelayer; a second conductive layer over the first conductive layer; athird conductive layer over the second conductive layer; a first organiccompound layer between the first conductive layer and the secondconductive layer; and a second organic compound layer between the secondconductive layer and the third conductive layer, wherein the firstorganic compound layer comprises: a photosensitized oxidation agent; anda substance, wherein the photosensitized oxidation agent is capable ofoxidizing the substance at least partly, wherein the second organiccompound layer comprises light emitting material, and wherein the secondconductive layer is capable of transmitting light.
 19. The memory deviceaccording to claim 18, wherein a voltage is applied to the firstconductive layer and the second conductive layer, wherein the lightemitting material emits light by recombination energy of holes andelectrons generated by the voltage, wherein the photosensitizedoxidation agent is excited by the light, and wherein the excitedphotosensitized oxidation agent is capable of oxidizing the substance atleast partly.
 20. The memory device according to claim 18, wherein aconductivity of the oxidized substance is different from a conductivityof the substance before oxidation.
 21. The memory device according toclaim 18, further comprising: a diode electrically connected to any oneof the first conductive layer and the third conductive layer.
 22. Thememory device according to claim 18, further comprising: a write circuitelectrically connected to a plurality of memory cells, wherein theplurality of the memory cells is arranged in a matrix form, and whereineach of the plurality of memory cells comprises the memory element. 23.The memory device according to claim 22, wherein each of the pluralityof memory cells further comprises a transistor.
 24. A semiconductordevice comprising: the memory device according to claim 18; a conductivelayer serving as an antenna; and a transistor electrically connected tothe conductive layer.
 25. The semiconductor device according to claim24, further comprising any one of a readout circuit, a power sourcecircuit, a clock generation circuit, a data modulation circuit, a datademodulation circuit, a control circuit and an interface circuit.
 26. Amemory device having a memory element comprising: a first conductivelayer; a second conductive layer; and an organic compound layer betweenthe first conductive layer and the second conductive layer, wherein theorganic compound layer comprises: a photosensitized reduction agent; anda substance, and wherein the photosensitized reduction agent is capableof reducing the substance at least partly.
 27. The memory deviceaccording to claim 26, wherein a voltage is applied to the firstconductive layer and the second conductive layer, wherein thephotosensitized reduction agent is excited by recombination energy ofholes and electrons generated by the voltage, and wherein the excitedphotosensitized reduction agent is capable of reducing the substance atleast partly.
 28. The memory device according to claim 26, wherein aconductivity of the reduced substance is different from a conductivityof the substance before reduction.
 29. The memory device according toclaim 26, further comprising: a diode electrically connected to any oneof the first conductive layer and the second conductive layer.
 30. Thememory device according to claim 26, further comprising: a write circuitelectrically connected to a plurality of memory cells, wherein theplurality of the memory cells is arranged in a matrix form, and whereineach of the plurality of memory cells comprises the memory element. 31.The memory device according to claim 30, wherein each of the pluralityof memory cells further comprises a transistor.
 32. A semiconductordevice comprising: the memory device according to claim 26; a conductivelayer serving as an antenna; and a transistor electrically connected tothe conductive layer.
 33. The semiconductor device according to claim32, further comprising any one of a readout circuit, a power sourcecircuit, a clock generation circuit, a data modulation circuit, a datademodulation circuit, a control circuit and an interface circuit.
 34. Amemory device having a memory element comprising: a first conductivelayer; a second conductive layer; and an organic compound layer betweenthe first conductive layer and the second conductive layer, wherein theorganic compound layer comprises: a light emitting material; aphotosensitized reduction agent; and a substance, and wherein thephotosensitized reduction agent is capable of reducing the substance atleast partly.
 35. The memory device according to claim 34, wherein theorganic compound layer comprises: a first layer comprising the lightemitting material; and a second layer comprising the photosensitizedreduction agent and the substance.
 36. The memory device according toclaim 34, wherein a voltage is applied to the first conductive layer andthe second conductive layer, wherein the light emitting material emitslight by recombination energy of holes and electrons generated by thevoltage, wherein the photosensitized reduction agent is excited by thelight, and wherein the excited photosensitized reduction agent iscapable of reducing the substance at least partly.
 37. The memory deviceaccording to claim 34, wherein a conductivity of the reduced substanceis different from a conductivity of the substance before reduction. 38.The memory device according to claim 34, further comprising: a diodeelectrically connected to any one of the first conductive layer and thesecond conductive layer.
 39. The memory device according to claim 34,further comprising: a write circuit electrically connected to aplurality of memory cells, wherein the plurality of the memory cells isarranged in a matrix form, and wherein each of the plurality of memorycells comprises the memory element.
 40. The memory device according toclaim 39, wherein each of the plurality of memory cells furthercomprises a transistor.
 41. A semiconductor device comprising: thememory device according to claim 34; a conductive layer serving as anantenna; and a transistor electrically connected to the conductivelayer.
 42. The semiconductor device according to claim 41, furthercomprising any one of a readout circuit, a power source circuit, a clockgeneration circuit, a data modulation circuit, a data demodulationcircuit, a control circuit and an interface circuit.
 43. A memory devicehaving a memory element comprising; a first conductive layer; a secondconductive layer over the first conductive layer; a third conductivelayer over the second conductive layer; a first organic compound layerbetween the first conductive layer and the second conductive layer; anda second organic compound layer between the second conductive layer andthe third conductive layer, wherein the first organic compound layercomprises: a photosensitized reduction agent; and a substance, whereinthe photosensitized reduction agent is capable of reducing the substanceat least partly, wherein the second organic compound layer compriseslight emitting material, and wherein the second conductive layer iscapable of transmitting light.
 44. The memory device according to claim43, wherein a voltage is applied to the first conductive layer and thesecond conductive layer, wherein the light emitting material emits lightby recombination energy of holes and electrons generated by the voltage,wherein the photosensitized reduction agent is excited by the light, andwherein the excited photosensitized reduction agent is capable ofreducing the substance at least partly.
 45. The memory device accordingto claim 43, wherein a conductivity of the reduced substance isdifferent from a conductivity of the substance before reduction.
 46. Thememory device according to claim 43, further comprising: a diodeelectrically connected to any one of the first conductive layer and thethird conductive layer.
 47. The memory device according to claim 43,further comprising: a write circuit electrically connected to aplurality of memory cells, wherein the plurality of the memory cells isarranged in a matrix form, and wherein each of the plurality of memorycells comprises the memory element.
 48. The memory device according toclaim 47, wherein each of the plurality of memory cells furthercomprises a transistor.
 49. A semiconductor device comprising: thememory device according to claim 43; a conductive layer serving as anantenna; and a transistor electrically connected to the conductivelayer.
 50. The semiconductor device according to claim 49, furthercomprising any one of a readout circuit, a power source circuit, a clockgeneration circuit, a data modulation circuit, a data demodulationcircuit, a control circuit and an interface circuit.